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Changes in the rice grain quality of different high-quality rice varieties released in southern China from 2007 to 2017
Accepted Manuscript Changes in the rice grain quality of different high-quality rice varieties released in southern China from 2007 to 2017 Yanhua Zeng, Xueming Tan, Yongjun Zeng, Xiaobin Xie, Xiaohua Pan, Qinghua Shi, Jun Zhang PII:
S0733-5210(18)30895-6
DOI:
https://doi.org/10.1016/j.jcs.2019.03.015
Reference:
YJCRS 2740
To appear in:
Journal of Cereal Science
Received Date: 25 November 2018 Revised Date:
22 March 2019
Accepted Date: 22 March 2019
Please cite this article as: Zeng, Y., Tan, X., Zeng, Y., Xie, X., Pan, X., Shi, Q., Zhang, J., Changes in the rice grain quality of different high-quality rice varieties released in southern China from 2007 to 2017, Journal of Cereal Science (2019), doi: https://doi.org/10.1016/j.jcs.2019.03.015. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Changes in the rice grain quality of different high-quality rice varieties
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released in southern China from 2007 to 2017
3 Yanhua Zeng1*, Xueming Tan*1, Yongjun Zeng1*, Xiaobin Xie1, Xiaohua Pan1, Qinghua Shi1, Jun
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Zhang2
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Breeding, Jiangxi Agricultural University, Nanchang 330045, P.R. China.
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Ministry of Education and Jiangxi Key Laboratory of Crop Physiology, Ecology and Genetic
Institute of crop sciences, Chinese Academy of Agricultural Sciences(CAAS), Beijing 100081,
P.R.China.
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E-mail addresses: [email protected]; [email protected]; [email protected].
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*
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Ecology and Genetic Breeding, Jiangxi Agricultural University, Zhimin Road, No.1101, Nanchang
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City, Jiangxi Province, China.
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Post code: 330045
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Corresponding author at: Ministry of Education and Jiangxi Key Laboratory of Crop Physiology,
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ACCEPTED MANUSCRIPT ABSTRACT
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High-quality rice varieties are planted widely in southern China. However, the changes in grain
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quality in the different high-quality rice varieties released in recent years are unclear. This study
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compared the grain quality changes and status of those varieties and presented proposals for future
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breeding. In the past 11 years, high-quality indica has significantly improved chalky rice rate (CRR),
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chalkiness degree (CD) but decreased head rice rate (HRR); amylose content (AC), gel consistency
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(GC) and length-to-width ratio (LWR) were improved only in indica hybrid rice. Most high-quality rice
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varieties grown in southern China are primarily indica rice. In contrast to indica rice, japonica rice had
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increased milling recovery, cooking and eating qualities (CEQ), but worsened significantly the physical
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appearance. For japonica rice, hybrid varieties exhibited a marked improvement in the rice quality for
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lower AC, higher GC and LWR compared with inbred varieties. A higher grain quality was observed in
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inbred varieties for indica rice due to lower CRR, CD and AC, higher HRR and GC. Our results
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suggested that we should be focused on improving the physical appearance quality for japonica rice
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and milling recovery, particularly CEQ for indica rice, for future high-quality rice breeding.
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Keywords: Southern China; High-quality rice varieties; Grain quality; Breeding objective.
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Abbreviations
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HRR: Head rice rate; CRR: Chalky rice rate; CD: Chalkiness degree; AC: Amylose content; GC: Gel
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consistency; LWR: Length-to width ratio
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Introduction Rice (Oryza sativa) is a staple cereal crop that is consumed by approximately 2/3 of the population
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of China (Duan and Zhou, 2013). Since rapid progress has been made in rice breeding, especially in
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rice crossbreeding, the grain yield potential of rice has been enhanced significantly over the past three
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decades (Zhang, 2016). Sufficient food production can satisfy the need to feed the Chinese population
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(Tester and Langridge, 2010). However, consumer food tastes are increasingly changing with the
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development of economic and quality of life levels, and thus the planting of high-quality rice has
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become more and more popular in rice production. Generally, there are the excellent comprehensive
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traits (including processing quality, appearance quality, cooking and eating properties, and nutritional
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qualities) of grain quality in high-quality rice, which meet the grade III national standard at least
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(GB/T17891-1999). High-quality rice can influence the market status and may increase production
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benefits (Yang et al., 2015; Qian, 2017). Therefore, breeding high-quality rice varieties is imperative.
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The grain quality of rice is a critical factor in determining its economic returns as well as the rice
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yields for farmers. There are several traits used to evaluate the rice quality, such as milling/processing
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appearance, cooking and eating properties, and nutritional qualities (Koutroubas et al, 2004), which are
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widely affected not only by environmental factors but also by genetic factors (Krishnan and Rao, 2005).
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Generally, it is common to evaluate the grain quality of rice by using many characteristics. The rice
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quality evaluation standards, such as NY20-1986 (1986) ‘quality edible rice,’ GB/T17891-1999 (1999)
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‘high quality paddy’, and NY/T593-2002 (2002) ‘cooking rice variety quality’, were promulgated by
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the Ministry of Agriculture of China (MAC). The high-quality traits in rice, including in indica and
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japonica, were divided into three grades according to both national and ministry standards
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(GB/T17891-1999, NY/T593-2002). For the international standards for ISO 7301-2011 and CAC
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quality has been gradually accepted for determining whether the rice quality is good or poor in relation
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to the economic value of a rice variety over time. The evaluation of good eating-quality rice includes
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the viscosity of rice starch, and the palatability, relish, odour, hardness, and texture of cooked rice
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(Balindong et al., 2018).
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Rice that generally contains indica (Oryza sativa L. subsp. indica) and japonica (Oryza sativa L.
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subsp. japonica) within both hybrid and inbred rice varieties (Tripp et al., 2010) is widely planted in
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China. The rice grain yield of China, especially for hybrid rice, has much higher potential compared
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with other countries, owing to the successful application of heterosis for rice production by Longping
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Yuan (Qian, 2017). There are indica and japonica rice varieties in southern China, which includes
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Zhejiang, Jiangxi, Hunan, Guangdong, Guangxi, and Fujian Provinces. The planting area of japonica
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rice has increased significantly in the others provinces in southern China with policy changes favouring
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indica rice over japonica rice with time (Zhang et al, 2013), not only in Zhejiang Province. In addition,
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breeding high-quality rice varieties has become a trend in recent decades (Yang et al., 2004; Xie and
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Zhang, 2018), and it has been dominate among the recently released varieties (Pang et al, 2016).
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Southern China is one of the major rice growing regions in China. However, changes in the grain
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quality traits of different types of high-quality rice that have been released in southern China for the
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past ten years are unclear.
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Recently, many breeding departments have screened and used excellent germplasm resources to
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breed high-quality rice groups that meet the grade III national standard for the rice quality, such as the
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indica cultivars Meixiangzhan2, Xiangyaxiangzhan and japonica cultivars Huruan1212 and
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ACCEPTED MANUSCRIPT Tianlongyou619 discussed in the Ministry of Agriculture and Rural Affairs of China (2018)1. There are
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also different breeding targets for rice quality traits for each province in southern China (Yang et al.,
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2004). We hypothesize that there are differences in the rice quality traits from 2007 to 2017 in the
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high-quality rice types for every province in southern China. Therefore, the objectives of this study
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were to 1) compare the changes and status of major quality traits in 710 high-quality rice varieties; 2)
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explore the differences in the quality characteristics of high-quality rice varieties for six provinces; and
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3) ascertain strategies for high grain-quality rice improvements in the future for southern China.
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2. Materials and methods
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2.1. Date collection and quality trait description
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We collated the major quality traits of 710 high-quality rice varieties that were selected from 1797
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rice varieties released in Jiangxi, Zhejiang, Fujian, Hunan, Guangxi and Guangdong Provinces. These
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traits were examined and approved by the provincial crop variety assessment committees (PCVAC) at
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the China rice data centre (www.ricedata.cn) from 2007 to 2017. The released high-quality rice
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varieties did not include glutinous rice and sterile lines. The selected high-quality rice varieties here
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were divided into four types including 25 japonica inbred rice varieties, 25 japonica hybrid rice
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varieties, 138 indica inbred rice varieties, and 522 indica hybrid rice varieties, according to the
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subspecies (japonica, indica) and breeding type (hybrid, inbred).
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The quality traits of the collected data primarily include the head rice rate (HRR, the percent of all
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intact head rice), chalky rice rate (CRR, the percent of all chalky grains), chalkiness degree (CD, the
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percentage of all chalky grain area relative to the total projected grain area), gel consistency (GC, the
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length of the gelatinous flow for gelatinized rice), amylose content (AC) and length-to-width ratio
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www.moa.gov.cn/ztzl/2018cg/gzbs/201805/t20180504_6141353.htm
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ACCEPTED MANUSCRIPT (LWR). The quality traits of the 1797 rice varieties were determined by the inspection and testing
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centre of the ministry of agriculture's rice and product quality supervision group according to the
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method of Wang et al. (2011) and Feng et al (2017). For HRR determined, the net weight of rice
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samples was firstly measured using a weighing balance, and after shelled, the brown rice was weighed,
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through milled, milled rice and head rice were both picked and weighed. The HRR was calculated as
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the percentage of head rice of the net weight of rice samples. The white belly/center/back or the all
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with above 20% on 100 milled grains selected were identified as chalky kernels, and CRR was
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expressed as the percentage of chalky rate of the milled grains samples. The mean of chalky kernels
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area of 10 rice chalky grains selected randomly was flattened and observed, and calculated as CD. The
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measure method for GC was as the following procedure: 100 mg flour was put in the culture tube, and
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dispersed in 0.2 mL of 0.025% thymol blue. Subsequently, 2.0 mL of 0.2 M KOH was added to the
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tubes, which was put into the boiling water for 8 min, covered with a glass marbles. The tube was
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placed on ice water to cool for 20 min, and then it was put down horizontally onto the table, to measure
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immediately the length of the rice gel in the tube. The AC was determined as described according to the
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methods of GB/T15683-2008: 100 mg of the samples was gelatinized in 9.0 mL of 1 M NaOH in a
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boiling water bath for 10 min, to disperse the starch. The solution was cooled at room temperature, and
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was diluted to the 100 ml volumetric flask. 3 mL of color developing agent containing 1.0 mL of ethyl
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alcohol and 2.0 mL of I2 reagent was added to 5 mL of the above solution, which was then measured at
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720 nm of absorbance. Ten grains of complete rice were lined up the measuring ruler to read the length,
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and then they were lined up side-by-side to read the width. The LWR was the ratio of length to width.
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The high-quality rice varieties that meet the grade Ⅲ national standard for each quality trait were
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selected under the ministry of agriculture standard GB/T17891-1999 ‘high quality rice’ or
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NY/T593-2002 ‘cooking rice variety quality’. In this study, japonica rice varieties are primarily planted in Zhejiang Province, and indica rice
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varieties are widely planted in the southern region of China, including the previously mentioned six
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provinces, which have adequate temperature, light and water resources. The annual average
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temperature is 15-24°C, the annual average rainfall is 950–2500 mm, the number of sunshine hours
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ranges from 1200–2500 h, and the active accumulated temperature above 10°C (AAT) is 5000–9000°C
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(AAT={mean daily temperature – 10} × number of days). The soils are primarily red and paddy soil.
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2.2. Statistical Analysis
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The significance of difference and variation coefficients for the high grain quality traits (in relation to
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the HRR, CRR, CD, GC, AC and LWR) between the rice varieties were both analysed statistically to
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calculate the least significant difference (LSD) values at the 0.05 probability level using IBM SPSS
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Statistics 19 (IBM Corp., Armonk, NY, USA). The variation coefficient for each quality trait with every
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year of release was calculated as the ratio of the standard deviation to the quality average value. The
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analysis of variance (ANOVA) of the subspecies (indica, japonica), breeding type (hybrid and inbred
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rice), year of release, and their interactions on high grain quality traits in rice varieties was performed
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using PROCESS MIXED to test the mean significance at the 0.05, 0.01 and 0.001 probability levels,
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according to the least significant difference (LSD). The relative (%) genetic gain of grain quality traits
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in the high-quality rice varieties released every year was calculated by regression analysis with the
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standard linear model, in accordance with the methods of Feng et al (2017).
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Yi= a+ bXi
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ACCEPTED MANUSCRIPT The Yi indicates the value for each grain quality trait, Xi indicates the year of cultivar i released, a
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menas the intercept of the equations, and b means the absolute slope. According to the released years
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for the six provinces, the rice varieties could be considered as being divided into three stages,
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2007-2010, 2011-2015, and 2016-2017.
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3. Results
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3.1. ANOVA of high grain quality traits in rice types
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There were differences in the grain quality traits affected by the subspecies, breeding type and year
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released and their two-factor interactions (Table 1). Significance was found for the subspecies in
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relation to the head rice rate, chalky rice rate, chalkiness degree, amylose content and length-to-width
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ratio. The head rice rate was also significantly affected by the breeding type and year of release.
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Significant interactions between the release year and the breeding type were observed for the head rice
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rate, amylose content, gel consistency and length-to-width ratio. A significant interaction between the
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release year and the subspecies was observed for the length-to-width ratio. Significant interactions
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between the breeding type and subspecies were observed for the chalky rice rate and the
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length-to-width ratio.
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3.2. Difference in high quality traits between japonica and indica rice types
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Japonica rice had a significantly higher head rice rate than indica rice (Table 2), and the same trends
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were observed between inbred varieties and hybrid varieties (P <0.05). Japonica rice also had a
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significantly higher chalky rice rate and chalkiness degree than indica rice (P <0.05). The same trends
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were observed in the indica hybrid compared with indica inbred rice, but no difference was found
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between the japonica rice types. The amylose content was significantly lower in japonica rice than in
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indica rice (P<0.05), and the same trend was observed between inbred and hybrid varieties for indica 8
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gel consistency than indica rice, and the difference in the gel consistency between hybrid and inbred
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rice for either rice type was inconsistent. Indica rice had a significantly higher length-to-width ratio
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than japonica rice, and the same trend was shown between hybrid and inbred varieties for japonica rice.
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3.3. Difference in the genetic gain of grain quality traits from 2007 to 2017
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The changes in grain quality of rice between indica and japonica varieties were varied from 2007
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to 2017 (Table 3). For japonica rice,.no significant change in grain quality traits was observed, except
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for the length-to-width ratio in japonica hybrid rice. By contrast, indica rice showed a significant
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decline in the head rice rate, chalky rice rate and chalkiness degree, suggesting an increase appearance
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quality (Table 3). For indica inbred rice, the length-to-width ratio was significantly decreased, whereas
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it was increased in indica hybrid rice. Moreover, a decreased amylose content and increased gel
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consistency were found for the indica hybrid rice, which might increase grain quality.
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3.4. Variation coefficient for different quality traits in high-quality rice varieties
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For the three stages of high grain quality rice released during the study periods (2007-2010,
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2011-2015, and 2016-2017), the chalky rice rate and chalkiness degree showed higher variation
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coefficients than the other quality indices. The variation coefficients for the head rice rate increased in
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the japonica varieties whereas decreased in the indica inbred rice over time. The japonica varieties
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showed decreased variation coefficients in the chalky rice rate, chalkiness degree, and amylose content,
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but an increased amylose content was observed in the indica rice and an increased chalky rice rate and
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degree of chalkiness were found in the indica inbred rice. The subspecies also showed reduced
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variation coefficients for gel consistency, but the variation coefficients for the length-to-width ratio
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were increased in the japonica rice and decreased in the indica rice (Table 4).
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Province among the six provinces. Relatively low variation coefficients for the chalky rice rate and
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chalkiness degree were observed in Zhejiang and Fujian Provinces, for amylase content in Fujian
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Province, and for gel consistency and length-to-width ratio in Guangxi Province. For indica hybrid rice,
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Hunan Province had lower variation coefficients for the head rice rate, gel consistency and
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length-to-width ratio than the other provinces, while the chalky rice rate and amylose content quality
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were reduced in Jiangxi Province. The variation coefficients in the degree of chalkiness decreased in
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Fujian and Zhejiang Provinces (Table 5).
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3.5. High-quality rice for each variety type in six provinces
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Jiangxi, Guangdong and Zhejiang Provinces had more released high-quality rice varieties than the
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other provinces from 2007 to 2017. For the three stages (2007-2010, 2011-2015, and 2016-2017),
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Jiangxi Province had relatively more high-quality rice varieties in the first stage, followed by
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Guangdong Province in both the second and the third stages. Hunan Province had relatively few
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high-quality rice varieties over time (Fig. 1A).
The percentage of high-quality rice varieties relative to all released rice varieties was higher than 30%
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in Guangdong, Jiangxi, Zhejiang and Fujian Provinces at each stage and in Guangxi Province at the
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first stage. Zhejiang Province had a relatively larger percentage of high-quality rice varieties at the first
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stage, with Jiangxi Province at the second stage and Guangdong Province in the third stage. Hunan
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Province had the smallest percentage of high-quality rice varieties at each stage (Fig. 1B).
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4. Discussion
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4.1. Change in grain quality traits for selected high-quality rice varieties
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value for rice (Lisle et al., 2000). In this study, the head rice rate in high quality inbred rice increased
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significantly (P <0.05) compared with high quality hybrid rice from 2007 to 2017, which was
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consistent with the results of Yang et al (2004). The japonica varieties had significantly higher head rice
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rates than the indica varieties for high-quality rice breeding types (Table 2). This result is similar to the
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results by Feng et al (2017), suggesting that japonica rice had good quality traits prior to indica rice.
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Additionally, the head rice rate in indica rice decreased significantly over time, but no change was
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observed for japonica rice. However, japonica rice showed a large difference in the head rice rate over
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time (Table 4). Thus, there is an urgent need to improve the head rice rate for both indica rice and
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japonica rice in the field of rice breeding.
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The chalky rice rate, chalkiness degree and length-to-width ratio can affect the appearance of rice
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and determine the appearance quality (Lisle et al., 2000). In particular, the chalky rice rate and
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chalkiness degree can become the major limiting factors for high-quality rice breeding (Du et al., 2007).
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Feng et al (2017) showed that japonica rice had a lower chalky rice rate and chalkiness degree
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compared with indica rice, but our results were not consistent with previous reports. It is well-known
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that high temperatures often occur during the grain filling period of japonica rice in southern China,
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which could affect the formation of chalkiness because japonica rice is sensitive to high temperatures
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(Zhang et al, 2016; Dou et al, 2018). Inbred varieties had significantly lower chalky rice rates and
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degrees of chalkiness than hybrid varieties for indica rice, indicating the excellent appearance
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advantage of indica inbred rice from previous rice breeding efforts, but there was no change in japonica
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rice. Interestingly, these quality traits decreased significantly in indica rice from 2007 to 2017 (Table 3),
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suggesting the great improvement in the appearance quality following high-quality rice breeding.
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However, indica rice also displayed higher variation coefficients for these qualities than japonica rice
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over time. Thus, these appearance quality traits should be improved through high-quality japonica rice
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breeding, and the status should be improved for high-quality indica rice breeding. In this study, high-quality japonica rice had a notably low length-to-width ratio, which suggests that
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it might make sense to breed with long-grain japonica rice in the future, especially for japonica inbred
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rice. In addition, the length-to-width ratio for indica inbred rice should further enhance the objectives
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of high-quality traits breeding, because this measure deceased significantly in past decades.
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The cooking and eating properties, namely, the gel consistency and amylose content, are principally
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related to traits involved in the cooking process (Bao et al., 2002). Furthermore, these traits are
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important selection factors for rice taste standards, and more and more people prefer to use the rice
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taste in evaluations (Fitzgerald et al., 2009). Feng et al (2017) proposed that japonica rice had a higher
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gel consistency and lower amylose content than indica rice, and Zhu et al (2004) demonstrated these
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results. Our study also showed similar results. However, these results differed between inbred and
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hybrid rice in both the japonica and indica varieties. The reason for this difference requires further
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study. According to the significantly increasing gel consistency and decreasing amylose content from
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2007 to 2017 for the indica hybrid rice, the gel consistency and amylose content quality traits might
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have room for breeding improvements in indica hybrid rice. In fact, high-quality indica hybrid varieties
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have good cooking and eating properties.
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4.2. Difference in grain quality traits between high-quality rice types in southern China
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Recently, high grain quality rice breeding has been become an important objective for breeders. It is
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necessary to carry out quality grading of rice to evaluate new rice lines released. Feng et al (2017)
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thought that japonica inbred rice had better-quality grain than indica hybrid rice, who collated data on 12
ACCEPTED MANUSCRIPT the japonica and indica rice released in China from 2000 to 2014. Zhu et al (2004) also proposed that
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japonica rice had a relatively high grain quality. However, in our study, even though japonica rice had
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higher head rice rate and gel consistency and lower amylose content compared with indica rice, the
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chalky rice rate and degree of chalkiness still increased significantly. These findings were not all
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consistent with Feng et al (2017) and Zhu et al (2004). Therefore, people prefer eating japonica rice to
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indica rice, because it possesses excellent softness and palatability in relation to the cooked rice,
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primarily owing to its relatively low amylose content and high gel consistency. In this study, in contrast
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to japonica rice, the indica hybrid rice had a lower chalky rice rate, degree of chalkiness and gel
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consistency and higher amylose contents and length-to-width ratios from 2007 to 2017 even though it
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had a lower head rice rate, suggesting that the breeding target for high-quality rice is to improve the
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appearance quality and the cooking and eating properties. In fact, the new agricultural industry
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standards for GB/T17891-2017(2017) ‘quality edible rice,’ which have not been promoted, will
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relatively reduce the standards for milling processing and appearance quality, but the standard grading
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was higher than the international standards for ISO 7301-2011 and CAC (Codex Alimentarius
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Commission). Our study found that the quality of hybrid rice was different from inbred rice between
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japonica and indica rice types, which differed from the findings of Feng et al (2017). Japonica hybrid
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rice had better cooking and eating qualities than japonica inbred rice, although it had a lower head rice
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rate; there were poor cooking and eating qualities in indica hybrid rice, although it had a higher chalky
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rice rate and degree of chalkiness. Therefore, there might be different improvement targets in the
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future.
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In this study, high variation coefficients for the quality traits were found in both the chalky rice rate
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and chalkiness degree for the six provinces in southern China, which is consistent with the findings of 13
ACCEPTED MANUSCRIPT earlier studies (Yang et al., 2004; Zhu et al, 2004; Feng et al, 2017). The chalky rice rate and chalkiness
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degree in indica rice showed relatively low variation coefficients in Zhejiang Province, suggesting a
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better climatic environment to benefit grain filling. Generally, the rice regions of northern China have
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better climatic conditions to adapt to breeding high-quality rice, in contrast to the rice region of
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southern China. However, in this study, there were also many high-quality rice varieties in southern
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China, especially in Guangdong and Jiangxi Provinces. These findings were related to the breeding
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targets and status. Most rice varieties in the top ten high-quality indica rice varieties were also bred by
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Guangdong Province as discussed recently at the conference of national high-quality rice tasting 1.
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Furthermore, more than 30% of the high-quality rice varieties were found in Guangdong, Jiangxi,
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Zhejiang, and Fujian Provinces in recent decades, suggesting the rapid breeding trends aimed at
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developing high-quality rice. Additionally, Guangdong and Jiangxi Provinces showed high and steady
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high-quality rice rates at the three stages.
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4.3. Challenge for high-quality rice breeding under eating habit changes
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Each quality trait affects the grain quality of rice. Japonica and indica rice are both planted in
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southern China, but there indica rice dominates due to the suitable climatic conditions and the eating
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habits of the southern people (Zhang et al, 2014). Indica rice has poor grain quality, especially in terms
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of cooking and eating qualities compared with japonica rice, resulting in the hardness and poor
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cohesiveness and viscosity of the cooked rice (Feng et al, 2017). Recently, southern consumers have
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also become increasingly fond of soft and palatable cooked rice, suggesting a breeding target for nice
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quality rice owing to changes in eating habits. In fact, Guangdong Province has been committed to
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excellent cooking and eating qualities in its rice breeding. Previous studies proposed that the milling
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and physical appearance quality of rice deteriorated significantly under increasing atmospheric CO2
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ACCEPTED MANUSCRIPT concentrations and ambient temperature (Wang et al., 2011; Madan et al., 2012; Dou et al, 2018).
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However, those conditions might lead to better trends in the taste of cooked rice in the future (Jing et al,
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2016). Additionally, the rice grain yields are also affected by elevated CO2 and temperatures (Satapathy
4
et al, 2014). Therefore, future breeding and agronomic management should primarily focus on
5
improving the cooking and eating quality of rice under elevated CO2 concentrations and temperatures,
6
and on synergies with the others quality traits and the grain yield.
7
5. Conclusions
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Southern China is a major rice production region, and it plays a very important role in enhancing
9
the high quality and grain yields of rice. In the last 11 years, most high-quality rice varieties have
10
primarily been based on indica rice in southern China, especially for Guangdong and Jiangxi Provinces.
11
The percentage of high-quality rice varieties in Guangdong, Jiangxi, Zhejiang, and Fujian Provinces is
12
relatively high. In contrast to high-quality indica rice, high-quality japonica rice has improved milling
13
recovery and cooking and eating quality, but it has a significantly worse physical appearance. There are
14
significant differences in the head rice rate between inbred and hybrid rice. For future high-quality rice
15
breeding, japonica rice should be improved with respect to its physical appearance quality, and indica
16
rice should be improved in relation to its milling recovery, particularly for the cooking and eating
17
quality.
18
Acknowledgements
19
Financial support for this work was provided by the National Key Research and Development Program
20
of China (2016YFD0300501), the Key Research and Development Program of Jiangxi Province
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(20171BBF60030), the Jiangxi Collaborative Innovation Center for Modern Agriculture Scientific
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Research (JXXTCX2015001-004, JXXTCX2017001-011), and the Jiangxi Department of Water
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ACCEPTED MANUSCRIPT Resources for Science and Technology Support Program (201820YBKT24).
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Qian, Q., 2017. Smart super rice. Sci. Chin. Life Sci. 60, 1-3.
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Yang, X.G., Chen, F., Lin, X.M., Liu, Z.J., Zhang, H.L., Zhao, J., Li, K.N., Ye, Q., Li, Y., Lv, S., Yang,
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P., Wu, W.B., Li, Z.G., Lal, R., Tang, H.J., 2015. Potential benefits of climate change for crop
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productivity in China. Agr. Forest Meteorol. 208, 76-84.
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Yang, Y.S., Chen, L.Y., Xu, Y.W., 2004. See the development of quality breeding in China from the
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change of rice quality evaluation standard. Hybrid Rice. 19, 5–10(in Chinese with English abstract).
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Zhang, C.Q., Zhou, L.H., Zhu, Z.B., Lu, H.W., Zhou, X.Z., Qian, Y.T., Li, Q.F., Lu, Y., Gu, M.H., Liu,
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Q.Q., 2016. Characterization of grain quality and starch fine structure of two japonica rice (Oryza
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2013. The productive advantages and formation mechanisms of ‘indica rice to japonica rice’. Sci. 18
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Agric. Sin. 46, 686-704 (in Chinese with English abstract). Zhang, Q.F., 2016. Brilliant fifty years of hybrid rice research in China (in Chinese). Chin. Sci. Bull. 61, 3730-3731. Zhang, Z., Wang, P., Chen, Y., Song, X., Wei, X., Shi, P.J., 2014. Global warming over 1960–2009 did
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increase heat stress and reduce cold stress in the major rice-planting areas across China. Eur. J.
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Agron. 59, 49-56.
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Zhu, Z.W., Chen, N., Wang, D.Y., Zhang, X.F., Yao,Q., Min, J., Liao, Q.Y., 2004. Analysis on variation
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and difference for rice quality traits among different types of rice. Chin. J. Rice Sci. 18, 315–320(in
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Chinese with English abstract).
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Table 1 ANOVA of high grain quality traits in rice Head rice
Chalky rice
Chalkiness
Amylose
Gel
Length-to
rate
rate
degree
content
consistency
width ratio
Factors 34.03***
Subspecies (indica, japonica)
24.981***
4.782*
0.05
0.03ns
2.369**
0.971ns
1.582ns
1.04ns
0.44ns
0.90ns
Subspecies × Breeding type
0.55ns
4.895*
0.445ns
0.24ns
0.06ns
15.41***
Subspecies × Year released
1.15ns
1.836ns
0.466ns
0.43ns
0.41ns
2.36**
2.499**
0.698ns
0.627ns
2.49**
2.36**
2.32*
0.37ns
0.472ns
0.34ns
0.33ns
0.04ns
1.35ns
Subspecies × Breeding type × Year released
ns
significant at a 0.05 probability level; ∗∗ significant at a 0.01 probability level; and ∗∗∗ significant at 0.001 probability level; and
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ns, not significant.
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Breeding type × Year released
ns
361.70***
3.50
Year released
ns
0.20ns
2.046
9.417
ns
6.18*
2.712
Breeding type (hybrid, inbred)
**
20
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Table 2 Differences in the mean quality traits between japonica and indica types of high-quality rice
Rice type
Head rice rate
Chalky rice
Chalkiness
Amylose
Gel consistency
Length-to-width
(%)
rate (%)
degree (%)
content (%)
(mm)
ratio
n 25
70.56a
27.96a
4.42a
16.36c
70.06bc
1.88c
Japonica hybrid
25
66.66b
25.96a
4.07a
15.69d
73.72a
2.21b
68.61
26.96
4.24
16.02
71.89
2.04
Indica inbred
138
64.96b
10.71c
2.36c
17.29b
70.31b
3.33a
Indica hybrid
522
61.53c
20.29b
3.59b
18.67a
68.43c
3.18a
63.25
15.50
2.97
17.98
69.37
3.26
Mean
Mean
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Japonica inbred
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The different lowercase letters followed by the value indicate significant differences at the 0.05 probability level.
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Table 3 Genetic gain (%) in grain quality traits in high-quality rice varieties Chalky rice Rice type
Head rice rate rate
Japonica inbred
ns
ns
Japonica hybrid
ns
ns
Indica inbred
-0.86***
-0.74***
Indica hybrid
-0.16*
-0.97***
Chalkiness
Amylose
degree
content
Length-to-width
ns
ns
ns
ns
ns
ns
ns
0.06***
-0.26***
ns
ns
-0.03**
-0.27***
-0.36***
0.65***
0.01*
Gel consistency ratio
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significant.
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∗ indicates significance at 0.05 probability level; ∗∗ indicates significance at 0.01 probability level; and ns indicates not
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Head rice rate
Chalky rice
Chalkiness
Amylose
Gel consistency
Length-to-width
(%)
rate (%)
degree (%)
content (%)
(mm)
ratio
2007-2010
6.07
44.16
53.37
5.70
5.93
18.11
Japonica
2011-2015
2.78
29.17
40.04
5.03
6.97
5.04
inbred
2016-2017
16.09
29.59
37.56
2.51
3.79
16.25
Mean
8.31ab
34.31b
43.66c
4.42b
5.56c
13.13a
2007-2010
4.62
85.23
50.42
1.67
12.66
3.09
Japonica
2011-2015
1.27
29.01
28.95
7.12
10.52
8.23
hybrid
2016-2017
6.40
31.85
38.71
4.19
7.10
9.03
Mean
4.09b
48.70ab
39.36c
4.33b
10.09b
6.78a
2007-2010
8.00
56.71
80.04
9.53
18.83
57.52
Indica
2011-2015
11.73
78.17
138.41
16.52
17.15
5.99
inbred
2016-2017
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Table 4 Difference in variation coefficients for quality traits in rice varieties registered from 2007 to 2017
6.24
101.79
119.52
17.06
10.78
6.01
8.66a
78.89a
112.65a
14.37a
15.59a
23.18a
2007-2010
9.81
60.35
92.11
14.12
16.88
13.78
2011-2015
9.14
53.91
88.23
15.89
18.14
9.59
2016-2017
9.14
68.86
70.50
15.30
14.56
8.51
Mean
9.36a
61.04a
83.61b
15.10a
16.53a
10.63a
Year
Indica hybrid
AC C
Mean
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Rice type
The different lowercase letters followed by a value indicates significant differences at the 0.05 probability level.
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Table 5 Changes in the variation coefficients for quality traits of high quality rice varieties in different provinces
Rice type
Head rice rate
Chalky rice
Chalkiness
Amylose
Gel consistency
Length-to-width
(%)
rate (%)
degree (%)
content (%)
(mm)
ratio
Zhejiang
8.57
37.73
45.34
6.31
5.90
15.18
Zhejiang
6.67
36.17
39.34
5.79
7.87
11.07
Zhejiang
5.07
38.62
49.50
14.84
77.56
4.88
Jiangxi
1.94
80.97
95.89
14.50
11.64
7.90
Hunan
6.29
48.22
61.58
5.88
15.60
14.43
Guangxi
6.03
91.32
98.55
6.04
3.48
4.79
Guangdong
10.37
73.25
121.09
14.95
13.51
7.52
5.15
45.58
40.63
2.91
22.23
—
8.47
46.38
51.99
15.59
18.25
20.11
8.27
46.29
64.00
12.83
17.17
8.15
Province
Japonica inbred Japonica
Fujian Zhejiang
AC C
Jiangxi
EP
Indica inbred
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hybrid
Hunan
6.32
55.42
56.02
18.48
9.52
6.95
Guangxi
7.61
61.06
66.75
18.10
12.09
9.85
Indica hybrid
Guangdong
9.18
55.99
90.38
18.17
14.72
8.63
Fujian
12.53
49.09
43.54
19.02
16.00
10.62
24
120 100
2007-2010
2011-2015
2016-2017
A
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Number of high-quality rice varieties
140
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80
AC C
60 40 20
0
Zhejiang
Jiangxi
Hunan
25
Guangxi
Guangdong
Fujian
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90
2007-2010
2011-2015
2016-2017
B
80 70 60 50 40 30 20 10 0
Jiangxi
Hunan
Guangxi
Guangdong
Fujian
SC
Zhejiang
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.Percentage of high-quality rice varieties (%)
100
AC C
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Fig. 1 Number(A) and percentage(B) of high-quality rice varieties in six provinces
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Highlights High-quality indica rice has significantly improved chalky rice rate and degree of chalkiness over time.
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High-quality japonica rice had increased milling recovery and cooking and eating qualities compared with high-quality indica rice.
For high-quality japonica rice, hybrid varieties exhibited a marked improvement in the rice quality; but
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a higher grain quality was observed in inbred varieties for high-quality indica rice.
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commercial or financial relationships that could be construed as a potential conflict of interest.
S0733-5210(18)30895-6
DOI:
https://doi.org/10.1016/j.jcs.2019.03.015
Reference:
YJCRS 2740
To appear in:
Journal of Cereal Science
Received Date: 25 November 2018 Revised Date:
22 March 2019
Accepted Date: 22 March 2019
Please cite this article as: Zeng, Y., Tan, X., Zeng, Y., Xie, X., Pan, X., Shi, Q., Zhang, J., Changes in the rice grain quality of different high-quality rice varieties released in southern China from 2007 to 2017, Journal of Cereal Science (2019), doi: https://doi.org/10.1016/j.jcs.2019.03.015. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Changes in the rice grain quality of different high-quality rice varieties
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released in southern China from 2007 to 2017
3 Yanhua Zeng1*, Xueming Tan*1, Yongjun Zeng1*, Xiaobin Xie1, Xiaohua Pan1, Qinghua Shi1, Jun
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Zhang2
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Breeding, Jiangxi Agricultural University, Nanchang 330045, P.R. China.
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Ministry of Education and Jiangxi Key Laboratory of Crop Physiology, Ecology and Genetic
Institute of crop sciences, Chinese Academy of Agricultural Sciences(CAAS), Beijing 100081,
P.R.China.
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E-mail addresses: [email protected]; [email protected]; [email protected].
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*
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Ecology and Genetic Breeding, Jiangxi Agricultural University, Zhimin Road, No.1101, Nanchang
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City, Jiangxi Province, China.
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Post code: 330045
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Corresponding author at: Ministry of Education and Jiangxi Key Laboratory of Crop Physiology,
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ACCEPTED MANUSCRIPT ABSTRACT
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High-quality rice varieties are planted widely in southern China. However, the changes in grain
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quality in the different high-quality rice varieties released in recent years are unclear. This study
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compared the grain quality changes and status of those varieties and presented proposals for future
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breeding. In the past 11 years, high-quality indica has significantly improved chalky rice rate (CRR),
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chalkiness degree (CD) but decreased head rice rate (HRR); amylose content (AC), gel consistency
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(GC) and length-to-width ratio (LWR) were improved only in indica hybrid rice. Most high-quality rice
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varieties grown in southern China are primarily indica rice. In contrast to indica rice, japonica rice had
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increased milling recovery, cooking and eating qualities (CEQ), but worsened significantly the physical
10
appearance. For japonica rice, hybrid varieties exhibited a marked improvement in the rice quality for
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lower AC, higher GC and LWR compared with inbred varieties. A higher grain quality was observed in
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inbred varieties for indica rice due to lower CRR, CD and AC, higher HRR and GC. Our results
13
suggested that we should be focused on improving the physical appearance quality for japonica rice
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and milling recovery, particularly CEQ for indica rice, for future high-quality rice breeding.
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Keywords: Southern China; High-quality rice varieties; Grain quality; Breeding objective.
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Abbreviations
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HRR: Head rice rate; CRR: Chalky rice rate; CD: Chalkiness degree; AC: Amylose content; GC: Gel
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consistency; LWR: Length-to width ratio
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Introduction Rice (Oryza sativa) is a staple cereal crop that is consumed by approximately 2/3 of the population
3
of China (Duan and Zhou, 2013). Since rapid progress has been made in rice breeding, especially in
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rice crossbreeding, the grain yield potential of rice has been enhanced significantly over the past three
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decades (Zhang, 2016). Sufficient food production can satisfy the need to feed the Chinese population
6
(Tester and Langridge, 2010). However, consumer food tastes are increasingly changing with the
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development of economic and quality of life levels, and thus the planting of high-quality rice has
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become more and more popular in rice production. Generally, there are the excellent comprehensive
9
traits (including processing quality, appearance quality, cooking and eating properties, and nutritional
10
qualities) of grain quality in high-quality rice, which meet the grade III national standard at least
11
(GB/T17891-1999). High-quality rice can influence the market status and may increase production
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benefits (Yang et al., 2015; Qian, 2017). Therefore, breeding high-quality rice varieties is imperative.
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The grain quality of rice is a critical factor in determining its economic returns as well as the rice
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yields for farmers. There are several traits used to evaluate the rice quality, such as milling/processing
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appearance, cooking and eating properties, and nutritional qualities (Koutroubas et al, 2004), which are
16
widely affected not only by environmental factors but also by genetic factors (Krishnan and Rao, 2005).
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Generally, it is common to evaluate the grain quality of rice by using many characteristics. The rice
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quality evaluation standards, such as NY20-1986 (1986) ‘quality edible rice,’ GB/T17891-1999 (1999)
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‘high quality paddy’, and NY/T593-2002 (2002) ‘cooking rice variety quality’, were promulgated by
20
the Ministry of Agriculture of China (MAC). The high-quality traits in rice, including in indica and
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japonica, were divided into three grades according to both national and ministry standards
22
(GB/T17891-1999, NY/T593-2002). For the international standards for ISO 7301-2011 and CAC
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ACCEPTED MANUSCRIPT (Codex Alimentarius Commission), the rice quality traits were not graded strictly. However, the eating
2
quality has been gradually accepted for determining whether the rice quality is good or poor in relation
3
to the economic value of a rice variety over time. The evaluation of good eating-quality rice includes
4
the viscosity of rice starch, and the palatability, relish, odour, hardness, and texture of cooked rice
5
(Balindong et al., 2018).
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Rice that generally contains indica (Oryza sativa L. subsp. indica) and japonica (Oryza sativa L.
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subsp. japonica) within both hybrid and inbred rice varieties (Tripp et al., 2010) is widely planted in
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China. The rice grain yield of China, especially for hybrid rice, has much higher potential compared
9
with other countries, owing to the successful application of heterosis for rice production by Longping
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Yuan (Qian, 2017). There are indica and japonica rice varieties in southern China, which includes
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Zhejiang, Jiangxi, Hunan, Guangdong, Guangxi, and Fujian Provinces. The planting area of japonica
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rice has increased significantly in the others provinces in southern China with policy changes favouring
13
indica rice over japonica rice with time (Zhang et al, 2013), not only in Zhejiang Province. In addition,
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breeding high-quality rice varieties has become a trend in recent decades (Yang et al., 2004; Xie and
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Zhang, 2018), and it has been dominate among the recently released varieties (Pang et al, 2016).
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Southern China is one of the major rice growing regions in China. However, changes in the grain
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quality traits of different types of high-quality rice that have been released in southern China for the
18
past ten years are unclear.
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Recently, many breeding departments have screened and used excellent germplasm resources to
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breed high-quality rice groups that meet the grade III national standard for the rice quality, such as the
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indica cultivars Meixiangzhan2, Xiangyaxiangzhan and japonica cultivars Huruan1212 and
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ACCEPTED MANUSCRIPT Tianlongyou619 discussed in the Ministry of Agriculture and Rural Affairs of China (2018)1. There are
2
also different breeding targets for rice quality traits for each province in southern China (Yang et al.,
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2004). We hypothesize that there are differences in the rice quality traits from 2007 to 2017 in the
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high-quality rice types for every province in southern China. Therefore, the objectives of this study
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were to 1) compare the changes and status of major quality traits in 710 high-quality rice varieties; 2)
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explore the differences in the quality characteristics of high-quality rice varieties for six provinces; and
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3) ascertain strategies for high grain-quality rice improvements in the future for southern China.
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2. Materials and methods
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2.1. Date collection and quality trait description
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We collated the major quality traits of 710 high-quality rice varieties that were selected from 1797
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rice varieties released in Jiangxi, Zhejiang, Fujian, Hunan, Guangxi and Guangdong Provinces. These
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traits were examined and approved by the provincial crop variety assessment committees (PCVAC) at
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the China rice data centre (www.ricedata.cn) from 2007 to 2017. The released high-quality rice
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varieties did not include glutinous rice and sterile lines. The selected high-quality rice varieties here
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were divided into four types including 25 japonica inbred rice varieties, 25 japonica hybrid rice
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varieties, 138 indica inbred rice varieties, and 522 indica hybrid rice varieties, according to the
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subspecies (japonica, indica) and breeding type (hybrid, inbred).
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The quality traits of the collected data primarily include the head rice rate (HRR, the percent of all
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intact head rice), chalky rice rate (CRR, the percent of all chalky grains), chalkiness degree (CD, the
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percentage of all chalky grain area relative to the total projected grain area), gel consistency (GC, the
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length of the gelatinous flow for gelatinized rice), amylose content (AC) and length-to-width ratio
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www.moa.gov.cn/ztzl/2018cg/gzbs/201805/t20180504_6141353.htm
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ACCEPTED MANUSCRIPT (LWR). The quality traits of the 1797 rice varieties were determined by the inspection and testing
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centre of the ministry of agriculture's rice and product quality supervision group according to the
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method of Wang et al. (2011) and Feng et al (2017). For HRR determined, the net weight of rice
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samples was firstly measured using a weighing balance, and after shelled, the brown rice was weighed,
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through milled, milled rice and head rice were both picked and weighed. The HRR was calculated as
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the percentage of head rice of the net weight of rice samples. The white belly/center/back or the all
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with above 20% on 100 milled grains selected were identified as chalky kernels, and CRR was
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expressed as the percentage of chalky rate of the milled grains samples. The mean of chalky kernels
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area of 10 rice chalky grains selected randomly was flattened and observed, and calculated as CD. The
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measure method for GC was as the following procedure: 100 mg flour was put in the culture tube, and
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dispersed in 0.2 mL of 0.025% thymol blue. Subsequently, 2.0 mL of 0.2 M KOH was added to the
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tubes, which was put into the boiling water for 8 min, covered with a glass marbles. The tube was
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placed on ice water to cool for 20 min, and then it was put down horizontally onto the table, to measure
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immediately the length of the rice gel in the tube. The AC was determined as described according to the
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methods of GB/T15683-2008: 100 mg of the samples was gelatinized in 9.0 mL of 1 M NaOH in a
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boiling water bath for 10 min, to disperse the starch. The solution was cooled at room temperature, and
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was diluted to the 100 ml volumetric flask. 3 mL of color developing agent containing 1.0 mL of ethyl
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alcohol and 2.0 mL of I2 reagent was added to 5 mL of the above solution, which was then measured at
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720 nm of absorbance. Ten grains of complete rice were lined up the measuring ruler to read the length,
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and then they were lined up side-by-side to read the width. The LWR was the ratio of length to width.
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The high-quality rice varieties that meet the grade Ⅲ national standard for each quality trait were
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selected under the ministry of agriculture standard GB/T17891-1999 ‘high quality rice’ or
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NY/T593-2002 ‘cooking rice variety quality’. In this study, japonica rice varieties are primarily planted in Zhejiang Province, and indica rice
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varieties are widely planted in the southern region of China, including the previously mentioned six
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provinces, which have adequate temperature, light and water resources. The annual average
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temperature is 15-24°C, the annual average rainfall is 950–2500 mm, the number of sunshine hours
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ranges from 1200–2500 h, and the active accumulated temperature above 10°C (AAT) is 5000–9000°C
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(AAT={mean daily temperature – 10} × number of days). The soils are primarily red and paddy soil.
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2.2. Statistical Analysis
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The significance of difference and variation coefficients for the high grain quality traits (in relation to
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the HRR, CRR, CD, GC, AC and LWR) between the rice varieties were both analysed statistically to
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calculate the least significant difference (LSD) values at the 0.05 probability level using IBM SPSS
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Statistics 19 (IBM Corp., Armonk, NY, USA). The variation coefficient for each quality trait with every
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year of release was calculated as the ratio of the standard deviation to the quality average value. The
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analysis of variance (ANOVA) of the subspecies (indica, japonica), breeding type (hybrid and inbred
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rice), year of release, and their interactions on high grain quality traits in rice varieties was performed
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using PROCESS MIXED to test the mean significance at the 0.05, 0.01 and 0.001 probability levels,
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according to the least significant difference (LSD). The relative (%) genetic gain of grain quality traits
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in the high-quality rice varieties released every year was calculated by regression analysis with the
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standard linear model, in accordance with the methods of Feng et al (2017).
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Yi= a+ bXi
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ACCEPTED MANUSCRIPT The Yi indicates the value for each grain quality trait, Xi indicates the year of cultivar i released, a
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menas the intercept of the equations, and b means the absolute slope. According to the released years
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for the six provinces, the rice varieties could be considered as being divided into three stages,
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2007-2010, 2011-2015, and 2016-2017.
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3. Results
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3.1. ANOVA of high grain quality traits in rice types
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There were differences in the grain quality traits affected by the subspecies, breeding type and year
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released and their two-factor interactions (Table 1). Significance was found for the subspecies in
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relation to the head rice rate, chalky rice rate, chalkiness degree, amylose content and length-to-width
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ratio. The head rice rate was also significantly affected by the breeding type and year of release.
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Significant interactions between the release year and the breeding type were observed for the head rice
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rate, amylose content, gel consistency and length-to-width ratio. A significant interaction between the
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release year and the subspecies was observed for the length-to-width ratio. Significant interactions
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between the breeding type and subspecies were observed for the chalky rice rate and the
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length-to-width ratio.
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3.2. Difference in high quality traits between japonica and indica rice types
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Japonica rice had a significantly higher head rice rate than indica rice (Table 2), and the same trends
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were observed between inbred varieties and hybrid varieties (P <0.05). Japonica rice also had a
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significantly higher chalky rice rate and chalkiness degree than indica rice (P <0.05). The same trends
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were observed in the indica hybrid compared with indica inbred rice, but no difference was found
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between the japonica rice types. The amylose content was significantly lower in japonica rice than in
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indica rice (P<0.05), and the same trend was observed between inbred and hybrid varieties for indica 8
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gel consistency than indica rice, and the difference in the gel consistency between hybrid and inbred
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rice for either rice type was inconsistent. Indica rice had a significantly higher length-to-width ratio
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than japonica rice, and the same trend was shown between hybrid and inbred varieties for japonica rice.
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3.3. Difference in the genetic gain of grain quality traits from 2007 to 2017
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The changes in grain quality of rice between indica and japonica varieties were varied from 2007
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to 2017 (Table 3). For japonica rice,.no significant change in grain quality traits was observed, except
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for the length-to-width ratio in japonica hybrid rice. By contrast, indica rice showed a significant
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decline in the head rice rate, chalky rice rate and chalkiness degree, suggesting an increase appearance
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quality (Table 3). For indica inbred rice, the length-to-width ratio was significantly decreased, whereas
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it was increased in indica hybrid rice. Moreover, a decreased amylose content and increased gel
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consistency were found for the indica hybrid rice, which might increase grain quality.
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3.4. Variation coefficient for different quality traits in high-quality rice varieties
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For the three stages of high grain quality rice released during the study periods (2007-2010,
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2011-2015, and 2016-2017), the chalky rice rate and chalkiness degree showed higher variation
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coefficients than the other quality indices. The variation coefficients for the head rice rate increased in
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the japonica varieties whereas decreased in the indica inbred rice over time. The japonica varieties
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showed decreased variation coefficients in the chalky rice rate, chalkiness degree, and amylose content,
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but an increased amylose content was observed in the indica rice and an increased chalky rice rate and
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degree of chalkiness were found in the indica inbred rice. The subspecies also showed reduced
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variation coefficients for gel consistency, but the variation coefficients for the length-to-width ratio
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were increased in the japonica rice and decreased in the indica rice (Table 4).
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Province among the six provinces. Relatively low variation coefficients for the chalky rice rate and
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chalkiness degree were observed in Zhejiang and Fujian Provinces, for amylase content in Fujian
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Province, and for gel consistency and length-to-width ratio in Guangxi Province. For indica hybrid rice,
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Hunan Province had lower variation coefficients for the head rice rate, gel consistency and
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length-to-width ratio than the other provinces, while the chalky rice rate and amylose content quality
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were reduced in Jiangxi Province. The variation coefficients in the degree of chalkiness decreased in
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Fujian and Zhejiang Provinces (Table 5).
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3.5. High-quality rice for each variety type in six provinces
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Jiangxi, Guangdong and Zhejiang Provinces had more released high-quality rice varieties than the
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other provinces from 2007 to 2017. For the three stages (2007-2010, 2011-2015, and 2016-2017),
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Jiangxi Province had relatively more high-quality rice varieties in the first stage, followed by
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Guangdong Province in both the second and the third stages. Hunan Province had relatively few
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high-quality rice varieties over time (Fig. 1A).
The percentage of high-quality rice varieties relative to all released rice varieties was higher than 30%
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in Guangdong, Jiangxi, Zhejiang and Fujian Provinces at each stage and in Guangxi Province at the
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first stage. Zhejiang Province had a relatively larger percentage of high-quality rice varieties at the first
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stage, with Jiangxi Province at the second stage and Guangdong Province in the third stage. Hunan
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Province had the smallest percentage of high-quality rice varieties at each stage (Fig. 1B).
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4. Discussion
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4.1. Change in grain quality traits for selected high-quality rice varieties
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Milling processing for high-quality rice primarily affects the milling quality. As a primary 10
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value for rice (Lisle et al., 2000). In this study, the head rice rate in high quality inbred rice increased
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significantly (P <0.05) compared with high quality hybrid rice from 2007 to 2017, which was
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consistent with the results of Yang et al (2004). The japonica varieties had significantly higher head rice
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rates than the indica varieties for high-quality rice breeding types (Table 2). This result is similar to the
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results by Feng et al (2017), suggesting that japonica rice had good quality traits prior to indica rice.
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Additionally, the head rice rate in indica rice decreased significantly over time, but no change was
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observed for japonica rice. However, japonica rice showed a large difference in the head rice rate over
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time (Table 4). Thus, there is an urgent need to improve the head rice rate for both indica rice and
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japonica rice in the field of rice breeding.
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The chalky rice rate, chalkiness degree and length-to-width ratio can affect the appearance of rice
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and determine the appearance quality (Lisle et al., 2000). In particular, the chalky rice rate and
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chalkiness degree can become the major limiting factors for high-quality rice breeding (Du et al., 2007).
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Feng et al (2017) showed that japonica rice had a lower chalky rice rate and chalkiness degree
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compared with indica rice, but our results were not consistent with previous reports. It is well-known
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that high temperatures often occur during the grain filling period of japonica rice in southern China,
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which could affect the formation of chalkiness because japonica rice is sensitive to high temperatures
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(Zhang et al, 2016; Dou et al, 2018). Inbred varieties had significantly lower chalky rice rates and
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degrees of chalkiness than hybrid varieties for indica rice, indicating the excellent appearance
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advantage of indica inbred rice from previous rice breeding efforts, but there was no change in japonica
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rice. Interestingly, these quality traits decreased significantly in indica rice from 2007 to 2017 (Table 3),
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suggesting the great improvement in the appearance quality following high-quality rice breeding.
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However, indica rice also displayed higher variation coefficients for these qualities than japonica rice
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over time. Thus, these appearance quality traits should be improved through high-quality japonica rice
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breeding, and the status should be improved for high-quality indica rice breeding. In this study, high-quality japonica rice had a notably low length-to-width ratio, which suggests that
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it might make sense to breed with long-grain japonica rice in the future, especially for japonica inbred
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rice. In addition, the length-to-width ratio for indica inbred rice should further enhance the objectives
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of high-quality traits breeding, because this measure deceased significantly in past decades.
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The cooking and eating properties, namely, the gel consistency and amylose content, are principally
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related to traits involved in the cooking process (Bao et al., 2002). Furthermore, these traits are
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important selection factors for rice taste standards, and more and more people prefer to use the rice
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taste in evaluations (Fitzgerald et al., 2009). Feng et al (2017) proposed that japonica rice had a higher
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gel consistency and lower amylose content than indica rice, and Zhu et al (2004) demonstrated these
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results. Our study also showed similar results. However, these results differed between inbred and
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hybrid rice in both the japonica and indica varieties. The reason for this difference requires further
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study. According to the significantly increasing gel consistency and decreasing amylose content from
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2007 to 2017 for the indica hybrid rice, the gel consistency and amylose content quality traits might
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have room for breeding improvements in indica hybrid rice. In fact, high-quality indica hybrid varieties
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have good cooking and eating properties.
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4.2. Difference in grain quality traits between high-quality rice types in southern China
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Recently, high grain quality rice breeding has been become an important objective for breeders. It is
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necessary to carry out quality grading of rice to evaluate new rice lines released. Feng et al (2017)
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thought that japonica inbred rice had better-quality grain than indica hybrid rice, who collated data on 12
ACCEPTED MANUSCRIPT the japonica and indica rice released in China from 2000 to 2014. Zhu et al (2004) also proposed that
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japonica rice had a relatively high grain quality. However, in our study, even though japonica rice had
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higher head rice rate and gel consistency and lower amylose content compared with indica rice, the
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chalky rice rate and degree of chalkiness still increased significantly. These findings were not all
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consistent with Feng et al (2017) and Zhu et al (2004). Therefore, people prefer eating japonica rice to
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indica rice, because it possesses excellent softness and palatability in relation to the cooked rice,
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primarily owing to its relatively low amylose content and high gel consistency. In this study, in contrast
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to japonica rice, the indica hybrid rice had a lower chalky rice rate, degree of chalkiness and gel
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consistency and higher amylose contents and length-to-width ratios from 2007 to 2017 even though it
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had a lower head rice rate, suggesting that the breeding target for high-quality rice is to improve the
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appearance quality and the cooking and eating properties. In fact, the new agricultural industry
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standards for GB/T17891-2017(2017) ‘quality edible rice,’ which have not been promoted, will
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relatively reduce the standards for milling processing and appearance quality, but the standard grading
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was higher than the international standards for ISO 7301-2011 and CAC (Codex Alimentarius
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Commission). Our study found that the quality of hybrid rice was different from inbred rice between
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japonica and indica rice types, which differed from the findings of Feng et al (2017). Japonica hybrid
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rice had better cooking and eating qualities than japonica inbred rice, although it had a lower head rice
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rate; there were poor cooking and eating qualities in indica hybrid rice, although it had a higher chalky
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rice rate and degree of chalkiness. Therefore, there might be different improvement targets in the
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future.
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In this study, high variation coefficients for the quality traits were found in both the chalky rice rate
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and chalkiness degree for the six provinces in southern China, which is consistent with the findings of 13
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degree in indica rice showed relatively low variation coefficients in Zhejiang Province, suggesting a
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better climatic environment to benefit grain filling. Generally, the rice regions of northern China have
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better climatic conditions to adapt to breeding high-quality rice, in contrast to the rice region of
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southern China. However, in this study, there were also many high-quality rice varieties in southern
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China, especially in Guangdong and Jiangxi Provinces. These findings were related to the breeding
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targets and status. Most rice varieties in the top ten high-quality indica rice varieties were also bred by
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Guangdong Province as discussed recently at the conference of national high-quality rice tasting 1.
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Furthermore, more than 30% of the high-quality rice varieties were found in Guangdong, Jiangxi,
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Zhejiang, and Fujian Provinces in recent decades, suggesting the rapid breeding trends aimed at
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developing high-quality rice. Additionally, Guangdong and Jiangxi Provinces showed high and steady
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high-quality rice rates at the three stages.
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4.3. Challenge for high-quality rice breeding under eating habit changes
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Each quality trait affects the grain quality of rice. Japonica and indica rice are both planted in
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southern China, but there indica rice dominates due to the suitable climatic conditions and the eating
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habits of the southern people (Zhang et al, 2014). Indica rice has poor grain quality, especially in terms
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of cooking and eating qualities compared with japonica rice, resulting in the hardness and poor
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cohesiveness and viscosity of the cooked rice (Feng et al, 2017). Recently, southern consumers have
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also become increasingly fond of soft and palatable cooked rice, suggesting a breeding target for nice
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quality rice owing to changes in eating habits. In fact, Guangdong Province has been committed to
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excellent cooking and eating qualities in its rice breeding. Previous studies proposed that the milling
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and physical appearance quality of rice deteriorated significantly under increasing atmospheric CO2
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However, those conditions might lead to better trends in the taste of cooked rice in the future (Jing et al,
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2016). Additionally, the rice grain yields are also affected by elevated CO2 and temperatures (Satapathy
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et al, 2014). Therefore, future breeding and agronomic management should primarily focus on
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improving the cooking and eating quality of rice under elevated CO2 concentrations and temperatures,
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and on synergies with the others quality traits and the grain yield.
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5. Conclusions
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Southern China is a major rice production region, and it plays a very important role in enhancing
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the high quality and grain yields of rice. In the last 11 years, most high-quality rice varieties have
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primarily been based on indica rice in southern China, especially for Guangdong and Jiangxi Provinces.
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The percentage of high-quality rice varieties in Guangdong, Jiangxi, Zhejiang, and Fujian Provinces is
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relatively high. In contrast to high-quality indica rice, high-quality japonica rice has improved milling
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recovery and cooking and eating quality, but it has a significantly worse physical appearance. There are
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significant differences in the head rice rate between inbred and hybrid rice. For future high-quality rice
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breeding, japonica rice should be improved with respect to its physical appearance quality, and indica
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rice should be improved in relation to its milling recovery, particularly for the cooking and eating
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quality.
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Acknowledgements
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Financial support for this work was provided by the National Key Research and Development Program
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of China (2016YFD0300501), the Key Research and Development Program of Jiangxi Province
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(20171BBF60030), the Jiangxi Collaborative Innovation Center for Modern Agriculture Scientific
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Research (JXXTCX2015001-004, JXXTCX2017001-011), and the Jiangxi Department of Water
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Agric. Sin. 46, 686-704 (in Chinese with English abstract). Zhang, Q.F., 2016. Brilliant fifty years of hybrid rice research in China (in Chinese). Chin. Sci. Bull. 61, 3730-3731. Zhang, Z., Wang, P., Chen, Y., Song, X., Wei, X., Shi, P.J., 2014. Global warming over 1960–2009 did
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increase heat stress and reduce cold stress in the major rice-planting areas across China. Eur. J.
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Agron. 59, 49-56.
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Zhu, Z.W., Chen, N., Wang, D.Y., Zhang, X.F., Yao,Q., Min, J., Liao, Q.Y., 2004. Analysis on variation
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and difference for rice quality traits among different types of rice. Chin. J. Rice Sci. 18, 315–320(in
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Chinese with English abstract).
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Table 1 ANOVA of high grain quality traits in rice Head rice
Chalky rice
Chalkiness
Amylose
Gel
Length-to
rate
rate
degree
content
consistency
width ratio
Factors 34.03***
Subspecies (indica, japonica)
24.981***
4.782*
0.05
0.03ns
2.369**
0.971ns
1.582ns
1.04ns
0.44ns
0.90ns
Subspecies × Breeding type
0.55ns
4.895*
0.445ns
0.24ns
0.06ns
15.41***
Subspecies × Year released
1.15ns
1.836ns
0.466ns
0.43ns
0.41ns
2.36**
2.499**
0.698ns
0.627ns
2.49**
2.36**
2.32*
0.37ns
0.472ns
0.34ns
0.33ns
0.04ns
1.35ns
Subspecies × Breeding type × Year released
ns
significant at a 0.05 probability level; ∗∗ significant at a 0.01 probability level; and ∗∗∗ significant at 0.001 probability level; and
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ns, not significant.
EP
*
TE D
Breeding type × Year released
ns
361.70***
3.50
Year released
ns
0.20ns
2.046
9.417
ns
6.18*
2.712
Breeding type (hybrid, inbred)
**
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Table 2 Differences in the mean quality traits between japonica and indica types of high-quality rice
Rice type
Head rice rate
Chalky rice
Chalkiness
Amylose
Gel consistency
Length-to-width
(%)
rate (%)
degree (%)
content (%)
(mm)
ratio
n 25
70.56a
27.96a
4.42a
16.36c
70.06bc
1.88c
Japonica hybrid
25
66.66b
25.96a
4.07a
15.69d
73.72a
2.21b
68.61
26.96
4.24
16.02
71.89
2.04
Indica inbred
138
64.96b
10.71c
2.36c
17.29b
70.31b
3.33a
Indica hybrid
522
61.53c
20.29b
3.59b
18.67a
68.43c
3.18a
63.25
15.50
2.97
17.98
69.37
3.26
Mean
Mean
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Japonica inbred
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Table 3 Genetic gain (%) in grain quality traits in high-quality rice varieties Chalky rice Rice type
Head rice rate rate
Japonica inbred
ns
ns
Japonica hybrid
ns
ns
Indica inbred
-0.86***
-0.74***
Indica hybrid
-0.16*
-0.97***
Chalkiness
Amylose
degree
content
Length-to-width
ns
ns
ns
ns
ns
ns
ns
0.06***
-0.26***
ns
ns
-0.03**
-0.27***
-0.36***
0.65***
0.01*
Gel consistency ratio
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significant.
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Head rice rate
Chalky rice
Chalkiness
Amylose
Gel consistency
Length-to-width
(%)
rate (%)
degree (%)
content (%)
(mm)
ratio
2007-2010
6.07
44.16
53.37
5.70
5.93
18.11
Japonica
2011-2015
2.78
29.17
40.04
5.03
6.97
5.04
inbred
2016-2017
16.09
29.59
37.56
2.51
3.79
16.25
Mean
8.31ab
34.31b
43.66c
4.42b
5.56c
13.13a
2007-2010
4.62
85.23
50.42
1.67
12.66
3.09
Japonica
2011-2015
1.27
29.01
28.95
7.12
10.52
8.23
hybrid
2016-2017
6.40
31.85
38.71
4.19
7.10
9.03
Mean
4.09b
48.70ab
39.36c
4.33b
10.09b
6.78a
2007-2010
8.00
56.71
80.04
9.53
18.83
57.52
Indica
2011-2015
11.73
78.17
138.41
16.52
17.15
5.99
inbred
2016-2017
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Table 4 Difference in variation coefficients for quality traits in rice varieties registered from 2007 to 2017
6.24
101.79
119.52
17.06
10.78
6.01
8.66a
78.89a
112.65a
14.37a
15.59a
23.18a
2007-2010
9.81
60.35
92.11
14.12
16.88
13.78
2011-2015
9.14
53.91
88.23
15.89
18.14
9.59
2016-2017
9.14
68.86
70.50
15.30
14.56
8.51
Mean
9.36a
61.04a
83.61b
15.10a
16.53a
10.63a
Year
Indica hybrid
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Mean
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Rice type
The different lowercase letters followed by a value indicates significant differences at the 0.05 probability level.
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Table 5 Changes in the variation coefficients for quality traits of high quality rice varieties in different provinces
Rice type
Head rice rate
Chalky rice
Chalkiness
Amylose
Gel consistency
Length-to-width
(%)
rate (%)
degree (%)
content (%)
(mm)
ratio
Zhejiang
8.57
37.73
45.34
6.31
5.90
15.18
Zhejiang
6.67
36.17
39.34
5.79
7.87
11.07
Zhejiang
5.07
38.62
49.50
14.84
77.56
4.88
Jiangxi
1.94
80.97
95.89
14.50
11.64
7.90
Hunan
6.29
48.22
61.58
5.88
15.60
14.43
Guangxi
6.03
91.32
98.55
6.04
3.48
4.79
Guangdong
10.37
73.25
121.09
14.95
13.51
7.52
5.15
45.58
40.63
2.91
22.23
—
8.47
46.38
51.99
15.59
18.25
20.11
8.27
46.29
64.00
12.83
17.17
8.15
Province
Japonica inbred Japonica
Fujian Zhejiang
AC C
Jiangxi
EP
Indica inbred
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hybrid
Hunan
6.32
55.42
56.02
18.48
9.52
6.95
Guangxi
7.61
61.06
66.75
18.10
12.09
9.85
Indica hybrid
Guangdong
9.18
55.99
90.38
18.17
14.72
8.63
Fujian
12.53
49.09
43.54
19.02
16.00
10.62
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120 100
2007-2010
2011-2015
2016-2017
A
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Number of high-quality rice varieties
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Zhejiang
Jiangxi
Hunan
25
Guangxi
Guangdong
Fujian
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2007-2010
2011-2015
2016-2017
B
80 70 60 50 40 30 20 10 0
Jiangxi
Hunan
Guangxi
Guangdong
Fujian
SC
Zhejiang
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.Percentage of high-quality rice varieties (%)
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Fig. 1 Number(A) and percentage(B) of high-quality rice varieties in six provinces
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Highlights High-quality indica rice has significantly improved chalky rice rate and degree of chalkiness over time.
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High-quality japonica rice had increased milling recovery and cooking and eating qualities compared with high-quality indica rice.
For high-quality japonica rice, hybrid varieties exhibited a marked improvement in the rice quality; but
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a higher grain quality was observed in inbred varieties for high-quality indica rice.
ACCEPTED MANUSCRIPT Conflict of Interest: The authors declare that the research was conducted in the absence of any
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commercial or financial relationships that could be construed as a potential conflict of interest.