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Symptom of the Shrunk-Grain Panicle and the Change Characteristics in Its Grain
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Agricultural Sciences in China 2008. 7(1): 10-18
ScienceDirect
January 2008
Symptom of the Shrunk-Grain Panicle and the Change Characteristics in Its Grain ZHANG Zu-jian, LANG You-zhong, PAN Mei-hong, YANG Jim-chang and ZHU Qing-sen Key Luborutory of Crop Genetics and Physiology o j Jiungsu Province, Yungzhou University, Yungzhou 225009, P.R.China
Abstract Over the past two years, an abnormal growth phenomenon called shrunk-grain panicle has occurred in a large area in Jiangsu Province of China. The phenomenon is described in details by figures and characters in this article. The method with a japonica rice Wuyujing 3 as the experimental material, the characteristics of grain morphology distribution and the grain weight were studied. Normal and shrunk-grain panicles were sampled from several representative areas. The length, width, and weight of the normal grains were distributed as regular, continuous, and single peaks. Plant growth typically had a right-leaning tendency. On the contrary, the distribution of the grain morphology and weight were irregular and nearly double that of the shrunk-grain panicle. The proportion of the cumulative distribution in the two kinds of peaks was closely related to the degree of shrunk-grain panicle. The article discusses the phenomenon’s symptoms, problems, and diagnosis.
Key words: rice, japonica, shrunk-grain panicle, symptom, grain weight, distribution
INTRODUCTION In recent years, an abnormal growth phenomenon of panicle and grain in japonica rice has occurred extensively in Jiangsu Province of China. Symptoms of this kind of disease on panicles are diminished chaff, and badly matched hook inside and outside husk, which result in split hulls and lightened grains. At the mature stage, these panicles erect because of decreased grain weight. Thus, it is often referred to as ‘erect panicle with shrunk-grain’, and is defined as ‘the shrunk-grain panicle’ in this study. Since the grain is abnormal and lightened, the rice yield reduced in different degrees and the field output can badly reduce by 50% or even more. Since the year 2000, the number of sites and the total area in north Jiangsu where the shrunk-grain panicle occured has increased. It has resulted in serious yield
losses, decreased incomes of peasant, and farmers’ doubt of the quality of the seeds provided. Furthermore, it may cause disharmony in the society at a rural area. At present, this phenomenon has already called attention of the department of agricultural services. As a kind of recently-appeared disease of rice in paddy field, the shrunk-grain panicle phenomenon has not been reported overseas. Although there are only a few domestic observation reports, these do not lead to systemic and general description (Zhang ef al. 2002; Chen et al. 2003; Wang et al. 2004, 2005). Concerning the shrunk-grain panicle phenomenon, we still know only little about the changes that have happened to the panicles and grains, and we have no clear standard for distinguishing and determining the nature of its symptom. This situation has blocked the study of the shrunk-grain panicle phenomenon. In this research, we have carried out more systemic and general observation on the
This paper is translaLed from its Chinese version in Scientiu Agriculruru Sinicu ZHANG Zu-jian. Ph D. Tel: +86-514-7972133. Mobile: 13338867606, E-mail: [email protected]. [email protected]
02008.CAAS. All rights reserved. Published by Elsevier Ltd.
Symptom of the Shrunk-Grain Panicle and the Change Characteristics in Its Grain
shrunk-grain panicle by sampling from several sites and analyzed the characteristics of the shrunk-grain panicle, the configuration character of the grain, and the grain weight. It will provide the foundation for further research on the causes and preventive measures of the shrunk-grain panicle.
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grains in the image were measured using Image Pro Plus, an image analyzing system. Distribution of the grain weight The weight of each single grain was measured separately, with a repetition of 200.
RESULTS
MATERIALS AND METHODS Tested cuIt ivars General variety of japonica rice Wuyujing 3,99-15 were used as tested cultivars.
Time and spot for sampling Continuous investigations on rice plant from milky ripe stage to maturity stage were carried out at several farms (Shanghai, Fangqiang, Dazhong, Baimahu, Gangfu, etc.) in the northern area of Jiangsu Province, China, in 2001, 2002. and 2003.
Sampling methods and contents Shrunk-grain panicles were sampled from farmlands where typical symptoms were found. At the same time, normal panicles were sampled for comparison. When typical shrunk-grain panicles were sampled, some seminormal panicles were sampled simultaneously to investigate the influence of the degree of symptoms on panicles. The main sampling sites included Yangzhou University experimental farm, Fangqiang farm in Yancheng, Baimahu farm in Huai’an, Agriculture Science Center of Lianyungang, etc., China.
Inquisition of panicle properties The panicle length and the number of grains per panicle were measured.
Measure of grain characters Distribution of the grain length and width The length and width of grains were measured using the imagescanning method. Grain samples (over 150 grains) were scanned to image, and then the length and width of the
The occurrence and the symptom of the shrunkgrain panicle Based on the inquisition from 2001 to 2003, it was clear that the occurrence of shrunk-grain panicles almost spread over all planting regions in the north and middle of Jiangsu, and that the repetition of incidence of this disease over years was less. The disease occurred in almost all japonica rice cultivars planted. Observation and comparison among sites in Shanghai farms in 2002 indicated that the Yanjing 9714 and all of 11 japonica rice cultivars caught the shrunk-grain panicle disease. The frequency of this disease differed among cultivars, ranging from 10 to 80%. In addition, investigation in Yangzhou, Huai’an, Yancheng, and Lianyungang showed that the shrunk-grain panicle disease was found in almost all late-growthjaponica rice cultivars as Wuyunjing 3, Wuxiangjing 9, Wuxiangjing 11, Wuxiangjing 14, Wuyunjing 7, Zhendao 88 and Zhendao 99, Huajing 1, Hanfeng 9, 99-15 and Guangling Xiangjing, etc., except for Sidao 10 which had smooth leaf and chaff. Further investigation is still required for protecting rice cultivars from the shrunk-grain panicle disease. Symptoms of shrunk-grain panicles When compared with the normal panicles in the mature stage, grains on shrunk-grain panicles were small, and the grain number was less. Fig.1-1 shows several different panicle samples of Wuyujing 3 with different degrees of the shrunk-grain panicle disease. Generally, the disease occurred at the top of the panicle first and made the grain appearance abnormal (Fig. 1-2). It was also found that the upper part of some diseased panicles was abnormal while the lower part appeared normal. Fig.1-3, 4 represents the shrunk-grain panicles of another cultivar 99-15. Similar to Wuyujing 3, the grains on shrunkgrain panicles diminished obviously and some diminished seriously with the splitting chaffs. Based on the degree of symptoms, the shrunk-grain panicle disease can be divided into three grades: (1) Mild case of shrunk-
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ZHANG Zu-jian er al.
Fig. 1 The appearance of shrunk-grain panicle in japonica rice. 1, the panicle of shrunk-grain panicle with different abnormity extent in Wuyujing 3; 2, the shape of shrunk-grain panicle in Wuyujing 3 at top of panicle; 3, the shape of shrunk-grain panicle in 99-15 at top of panicle; 4, the shape of normal panicle and of shrunk-grain panicle in 99-15; 5, the grain of shrunk-grain panicle in Wuyujing 3; 6, the milled rice of shrunk-grain panicle in Wuyujing 3.
82008, CAAS. All rights resewed.Publishedby Elsevier Ltd.
SvmDtom of the Shrunk-Grain Panicle and the Change Characteristics in Its Grain
grain panicles. Only a few grains on the top part of the panicle were shrunk and split, and the panicle length and the grain number per panicle were about 90% of the normal ones. (2) Medium case of shrunk-grain panicles. There were more shrunk and split grains on the upper part of the panicle, but the grains on the lower part of the panicle were more natural grains. The panicle length and grain number declined to 70430% of the normal ones, and the phenomenon was seen clearly. (3) Serious case of shrunk-grain panicles. Shrunk and split grains were spread all over the panicle. The panicle length and grain number decreased to less than 70% of the normal ones. These abnormal panicles could be seen easily in fields. As seen in the following images, the three different cases of abnormal panicles are very obvious. Table 1 shows the comparison of the normal and the diseased panicles in length and the grain number per panicle, in Wuyujing 3. In the normal panicle, the average length was 14.66 cm and the grain number per panicle was about 98. There was no significant difference between the normal panicles and the mild case of shrunk-grain panicles. In the medium case of shrunkgrain panicles, the length of the panicles decreased by 11.7% and the number of grains decreased by about 19.6%. In the serious case, the panicle length and the grain number per panicle were about 69.6 and 60.4% of the normal ones, respectively. Table 1 Differing characteristics of the shrunk-main Danicle') Category Normal panicle Low shrunk-grain panicle Middle shrunk-grain panicle High shrunk-grain panicle 1)
Length of panicle (cm) Spikelets per panicle 14.66 a 98.2 a 95.1 a 14.33 a 12.94 h 79.0 b 59.3 c 10.20 c
Significant degree at 0.05 by LSD.
The appearance of shrunk-grain panicle Fig. 1-5 shows the comparison of appearance between normal grains and shrunk-grains. It was clear that in addition to the shrunk size of grain, there were grave clefts on chaffs of shrunk grains. This kind of cleft was hypostatic, dissimilar to the ones that were caused by excessive filling in the later mature period, since shrunkgrain panicle was more grave and obvious. Moreover, the color of rice inside the split chaff was usually changed and was easy to distinguish. The more serious the shrunk-grain panicle disease, the more obvious was the grain shrunk and split. Besides, several shrunk grains had abnormal appearance in different degrees. Fig. 1-6 shows the difference of brown rice between
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the normal and shrunk grains. The brown rice inside shrunk grains were small and abnormal, in gray or brown colors, which distinguished them from smooth, transparent normal ones. Population appearance of the shrunk-grain panicles The population appearance of the shrunkgrain panicles in paddy field has some difference according to disease degrees. When compared to the panicle layer of the normal rice plant which looks orderly and heavy, the shrunk-grain panicles of diseased rice plant in paddy field looks disorderly, light and small, so shrunk-grain panicles in severe disease paddy field could be easily seen by naked eyes. By observing the seriously-diseased population, it was clear that the same stub and the same hill have the same disease. Namely, panicles in the same hill were highly correlated. Thus, in paddy fields, the shrunk-grain panicle disease usually occurred irregularly and unevenly. In the hills where the disease was serious, there were slight differences among panicles within the same hill, but in lightly-diseased hills, the degree of disease differed among panicles, and thus, some panicles may be normal, while others be very abnormal.
Distribution of grain shape indices Distribution of normal grain shape indices Fig.2 shows the distribution curve of the length and width of normal grains of Wuyujing 3 planted in Yangzhou University agricultural experimental farm. It was clear that both distributions of the grain length and width showed to be single peaked curves with distinct right skew, which were different to mormal distribution. Hence, we can conclude that under the normal growth condition, the length and width of the grains have regular distribution. Distribution of shrunk grain Fig.3 shows the distribution curves of the appearance of the shrunk grains grown in three different regions in Jiangsu Province with mixed samples. When compared with the single peaked regular distribution of the normal grains, the distribution of the length and width of shrunk grains from all three regions were dispersed, bimodal curves. That is to say, there was a higher distribution center and a lower distribution center on each distribution curve of shrunk grains for one sample, caused by two classes of grains each sample, one was seriously diseased grains, and the other was relatively normal ones. 02008, CAAS. All rightsreserved Publishedby Elsevier Ltd.
ZHANG Zu-iian ef al.
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Comparative analysis of the shape and weight for shrunk grains
Fig. 2 The frequency distribution of the shape of the normal grain in Wuyujing 3.
To further find the emerged characters for symptom of shrunk grains, the subnormal grains (the least disease degree) were analyzed, and the results in Fig.4 shows that the distribution of lightly-diseased grains had similar bimodal curves, but the peak that represents normal grains was considerably higher, and on the contrary, abnormal grains were relatively fewer.
Distributionfor weight of shrunk grains Fig.5 shows the distribution for the grain weight of 2 normal grain samples and 3 shrunk grain samples of Wuyujing 3, harvested from different sites. Similar to the frequency distribution for the grain shapes, the distribution curves for grain weight of normal grains were typically single peaked, distinct right skewed and continuous, whereas for shrunk grains, the curves were nearly double peaked. In the mild case of shrunk grain panicles, the proportion of abnormal grains was little. It was clear that the proportion of the distribution in the two kinds of peaks was closely related to the degree of shrunk-grain disease, especially for the peak that represented the abnormal grains. The higher the degree of the disease, the larger were the peak value and the cumulative distribution.
Table 2 shows the average value and coefficient of variation of the normal and shrunk grains. It can be seen that, for normal panicle of japonica rice Wuyujing 3, which was grown in Yangzhou University, the grain weight was about 0.027 g/grain, with a coefficient of variation (CV) of 6-8% for the weight and 4% for the width and length. When compared with the normal grains, the length and width of the shrunk grains decreased with a larger coefficient of variation. The reduction of width and the increment of CV were considerably larger than those observed in the length of the shrunk grains, showing that the reduction of width was the indicator of the shrunk-grain disease. The grain weight was similar to the width. When the shrunkgrain disease occurred, the weight of the grain became lightened, and the irregularity of the grain weight was magnified.
DISCUSSION The history and its present condition of the phenomenonof the shrunk-grain panicle The formal report on the phenomenon of the shrunkgrain panicle was limited in Jiangsu Province of China, and the research on it is still very little (Pan et al. 2002; Zhang 2002a, b; Chen et al. 2003; Fan et al. 2003, 2004; Gu et al. 2003; Wang et al. 2002, 2003, 2004, 2005; Zhang 2005; Lianyungan Seed Station 2002). In fact, as early as in 1966, there was a report on the raised head panicle in Nongken 58 in Zhenjiang, Jiangsu Province (Cui 1966). According to the report, abnormal rice plants had the panicle length reduced, the grains diminished, the chaff split, and the rice was small with color changes. From the phenomenon, it can be seen that it was similar to the shrunk-grain panicle described in the present article. But at that time, the misuse of water and fertilizer was thought to be the main reason. Besides, although there was no formal report, people in Zhenjiang Academy of Agricultural Sciences once discovered shrunk-grain panicles, which caused the output reduction in a part of the fields. However, no deep investigation and research was done on this issue. In
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SvmDtorn of the Shrunk-Grain Panicle and the Change Characteristics in Its Grain
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Fig. 3 The frequency distribution of shape in shrunk-grain panicle.
Fig. 4 The frequency distribution of shape in the slight shrunk-grain panicle.
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ZHANG Zu-jian et al.
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Fig. 5 The distribution of grain weight in the normal grain and shrunk-grain panicle. Table 2 Comparison of the shape and weight of grain in a normal panicle with the shrunk-grain panicle
~,-"... Normal -mains from Yangzhou - Uni.
Tbnr nf mli"
.,=-I.
Grains of shrunk-grain panicle from Fangqiang Grains of shrunk-grain panicle from Baimahu Grains of shrunk-grain panicle from Dazhong
Length Average (mm) 6.31 5.88 5.82 5.73
CV (%) 3.90 6.01 6.11 8.89
the 1990s, shrunk-grain panicles occurred sporadically in some areas in Jiangsu Province, including Zhenjiang, Huai'an, Yancheng cities; however, the area and damage were both extremely small to catch the attention of researchers. Until the recent five years, the phenomenon became worse and occurred in all cultivars of japonica rice in Jiangsu Province, causing
Width Average (mm) 3.30 2.76 2.69 2.64
cv (%) 4.32 11.28 9.15 15.25
Grain weight Average (g) CV (%) 0.0271 8.66 0.0234 15.64 0.0227 11.62 0.0232 19.12
serious reduction of yield. Furthermore, the cause and mechanism of the shrunk-grain panicle have not been clarified yet, and it has been difficult for agriculture technique services and seed management services to judge and prevent the disease. According to our investigation, this disease is usually centralized in the north of Jiangsu Province, in-
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Symptom of the Shrunk-Grain Panicle and the Chanpe Characteristics in Its Grain
cluding Yangzhou, Taizhou, Huai’an, Yanchen, Lianyungang cities, and some regions in Nantong and Xuzhou.
The Chinese name and English name of the shrunk-grain panicle Several agricultural researchers have paid attention to the occurrence of the shrunk-grain panicle. There are also a few reports about people’s attempts to prevent it (Wang et al. 2004,2005; Zhang et al. 2005; Yang et al. 2005). There were various reports regarding the name of this phenomenon. Considering that some informal names have caused inconvenience, a unified and formal name was necessary for in-depth studies about the reasons and measures to prevent it. Currently, some names can be seen, for example, ‘the small panicle’ ‘the head-raising panicle’, ‘shrunk-grain panicle’, ‘shrunk-grain and raising panicle’, and so on. Among these names, ‘small panicle’ can easily confuse people with small panicles with normal morphology. ‘Raising panicle’ can lead to a misunderstanding that the phenomenon was caused by the bad environment, such as high or low temperature, or lack of water (Wang et al. 1995; Zhu et al. 2005). ‘Raise panicle’ can also be easily confused with modern cultivars ‘erect panicle’ (Xu et al. 1996; Zhang et al. 2002). Based on its symptom, we thus define it as ‘shrunk-grain panicle’.
The diagnosis of the shrunk-grainpanicle and the establishment of its criterion We have recognized the morphological characteristics of ‘shrunk-grain panicle’, as mentioned above. The symptom was obvious when the degree of shrunk-grain panicle was severe; the whole panicle length, grain length, and grain width were shortened, and the chaffs were split. As for the distribution of abnormal grains on the panicles, the upper part was more seriously damaged than the lower part. To the whole tiller and community, the panicles were erect because of lightened weight. In the field of the mild case of the disease, the symptom was lighter. There is still no suitable criterion to judge the occurrence of shrunk-grain panicles. For example, split in chaff is an important character in shrunk-grains, but in several japonica rice cultivars, it may happen because of fine growth in the late stage.
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To distinguish the disease, all kinds of characteristics of shrunk-grains must be combined. This research provides detailed descriptions about the distribution for grain length, width, and weight in shrunk-grainpanicles. From the results, it can be seen that similar to the other researches (Kuang et al. 2005), the frequency distribution of normal grains was a single peak curve, but that of the shrunk grains was a double-peak curve. By analyzing the abnormity of the distribution curves, it was found that the weights of most grains in diseased panicles are 70-80% of the normal ones. It suggests that besides the split chaff character, the criteria of the shrunk-grain can be defined as about 80% of the normal grain (for grain length, less than 85% of normal grain; for width, 80%;for grain weight, less than 85%). In addition, although the shrunk-grain panicle disease may also cause reduction of the setting rate and the grain number per panicle, it is difficult to provide quantitative criterion for the large scope of variation.
The possible nosogenesis for the shrunk-grain panicle The problems that must be dealt with include the cause and prevention of the shrunk-grain panicle. Now, there are some reports about the reason of the shrunk-grain panicle. (1) Wireworm. Our research team have the data that there were considerably more wireworms in the diseased grains (The result will be reported later). But several questions still remain to be answered: The wireworm has existed for several years in rice (Duan and Wu 2002), but why has the shrunk-grain panicle disease occurred only in recent two years? For two fields nearby with the same variety and same cultivation, why is one field heavily diseased and the other normal? (2) Pathogen. Some people suggest that it may be a new kind of rice disease caused by germs or virus, but there is no convictive evidence. (3) Deterioration of cultivars. Farmers and agricultural services often have this viewpoint. However, the experiment that the same diseased seeds grew up into normal plants in Hainan Province of China, and the fact that there are obvious differences between plants grown in different areas with the same seeds, showed that it could not be caused by heredity factors. (4)Insecticide and herbicide. Although this point of view has been accepted by several researchers, there has been no direct evidence yet. ( 5 )
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Water deficit. It is thought that in the growing period, especially, the meiosis period, the water shortage can seriously cause shrunk-grain panicles. However, in several fields with heavily-damaged shrunk-grain panicles, water management was well done, revealing that water deficit cannot be the main nosogenesis for this disease. Though the research of the shrunk-grain panicle has been carried out for two years, it is still early to provide an affirmative conclusion on its nosogenesis, and considerable study still needs to be done to solve the shrunkgrain panicle. An in-depth study on the nosogenesis for this disease must be urgently done at present.
Acknowledgements This study was supported by the program of Agricultural Three-Project of Jiangshu Province, China (SX2002-08 1).
References Chen H C, Wang Q M, Sun J Q, Bao G X, Chen G Y, Xu P. 2003. The investigation on “Shrunk-grain Panicle” in rice in 2001. Agricultural Technology in Shanghai, (4),23-25. (in Chinese) Cui J L. 1966. Conquers the shrunk-grain panicle, achieves higher grain yield. Acta Agronomica Sinica, (2), 13-14. (in Chinese) Duan Y X, Wu G. 2002. The Prevention of Disease for Plant Parasitic Nematodes. China Agricultural Scientech Press, Beijing. (in Chinese) Fan L Z, Li X X, Zhang S Y, Wang N Z. 2003. The observation for the symptoms of “shrunk-grain Panicle” caused by dry and tine nematodes rice. Plant Protection Technology and Extension, 23, 18-19. (in Chinese) Fan L Z, Li X X, Sun Y W, Lin H F. 2004. The reasons and prevention about middle ripe and dense panicle type of japonica rice. China Plant Protection, 24, 10-11. (in Chinese) Gu Y M, Li B S, Zhong S H. 2003. “Shrunk-grain Panicle” in rice can’t be considered as a problem of seeds. China Seeds, (l), 27. (in Chinese) Kuang F C, Zeng K, Xiao L T, Ding J H, Li H S. 2005. Study on difference of grain weight distribution in two-line supperhybrid rice. Chinese Agricultural Science Bulletin, 21, 193194. (in Chinese) Lianyungang Seed Station. 2002. The preliminary certification about “shrunk-grain Panicle” in rice. Agriculture Science Communication, (6), 9. (in Chinese) Pan Q M, Gu S Y, Zhang X Z. 2002. The main reasons and its prevention for the formation of “Shrunk-grain Panicle” in rice. China Rice, (4), 32. (in Chinese)
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Wang Z, Gu Y J, Yu H L, Shi H Y, Gao Y Z. 1995. Studies on the cause of formation of deformed kernel of wild abortion type male sterile line in rice. Scientia Agricultura Sinica, 28,263 1. (in Chinese) Wang Z M, Zhou F M, Chen F H. 2002. Analysis of the reasons for the formation of “Shrunk-grain Panicle” in rice. Agricultural Science in Jiangsu, (2), 13-14. (in Chinese) Wang Z M, Zhou F M, Lu Y L, Lu H F, Lu X L, Xu M B, Chen Z Y, Liu Y F, Xu S . 2003. Studies on the reasons and its prevention for the formation of “Shrunk-grain Panicle” in rice in Jiangsu. Agricultural Science in Jiangsu, (5), 1-6. (in Chinese) Wang Z M, Zhou F M, Lu H F, Lu X L, Chen Z Y, Liu Y F, Wei W. 2004. Studies on the reasons and their preventions for the formation of “shrunk-grain Panicle” in rice in Jiangsu Province. Agricultural Science in Jiangsu, (3), 34-38. (in Chinese) Wang Z M, Zhou F M, Lu Y L, Lu H F, Zhang A C, Xu M B, Chen Z Y. 2005. Studies on the reasons for the formation of “shrunk-grain Panicle” and applications of its control technology. Agricultural Science in Jiangsu, (3), 55-60. (in Chinese) Xu Z J, Chen W F, Zhou H F, Zhang L B, Yang S L. 1996. The character of physiology-ecology and application foreground of erect panicle type of rice. Chinese Science Bulletin, 41, 1122-1 126. (in Chinese) Yang H F, Wang Z Y, Ji M X, Wu H Z. 2005. The effect of the 6% prescriptions of Shamindan on preventing “shrunk-grain Panicle”. Agricultural Science in Jiangsu, (2), 62-63. (in Chinese) Zhang W Z, Xu Z J, Chen W F, Zhang L B, Jin X H, Wu X D. 2002. The research progress on erect panicle type of rice. Journal of Shenyang Agricultural University, 33,47 1-475. (in Chinese) Zhang X Z. 2002a. The investigation and analysis on the main reasons for “shrunk-grain Panicle” in rice. Agriculture Science Communication, (6). 8-9. (in Chinese) Zhang X Z. 2002b. The primary reasons and preventions for the formation of “Stand erect panicle” in rice. Agricultural Science in Jiangsu, (Suppl.), 27-28. (in Chinese) Zhang Z J, Fang M K, Wang Z M, Mao C Y, Chen H D, Yuan S Z, Bo L S, Zhou C H, Zhu Q S, Yang J C. 2005. Preliminary studies on the cause of “Shrunk-gain Panicle” in rice. Journal of Yangzhou University (Agricultural and Life Science Edition), 26, 60-65. (in Chinese) Zhu C L, Xiao Y H, Wang C M, Jiang L, Zhai H Q, Wan J M. 2005. Mapping QTLs for heat tolerance during grain filling in rice. Chinese Journal of Rice Science, 19, 117-121. (in Chinese) (Edited by ZHANG Yi-min)
82008, CAAS. All rights resewed.Publishedby ElsevierLtd.
Agricultural Sciences in China 2008. 7(1): 10-18
ScienceDirect
January 2008
Symptom of the Shrunk-Grain Panicle and the Change Characteristics in Its Grain ZHANG Zu-jian, LANG You-zhong, PAN Mei-hong, YANG Jim-chang and ZHU Qing-sen Key Luborutory of Crop Genetics and Physiology o j Jiungsu Province, Yungzhou University, Yungzhou 225009, P.R.China
Abstract Over the past two years, an abnormal growth phenomenon called shrunk-grain panicle has occurred in a large area in Jiangsu Province of China. The phenomenon is described in details by figures and characters in this article. The method with a japonica rice Wuyujing 3 as the experimental material, the characteristics of grain morphology distribution and the grain weight were studied. Normal and shrunk-grain panicles were sampled from several representative areas. The length, width, and weight of the normal grains were distributed as regular, continuous, and single peaks. Plant growth typically had a right-leaning tendency. On the contrary, the distribution of the grain morphology and weight were irregular and nearly double that of the shrunk-grain panicle. The proportion of the cumulative distribution in the two kinds of peaks was closely related to the degree of shrunk-grain panicle. The article discusses the phenomenon’s symptoms, problems, and diagnosis.
Key words: rice, japonica, shrunk-grain panicle, symptom, grain weight, distribution
INTRODUCTION In recent years, an abnormal growth phenomenon of panicle and grain in japonica rice has occurred extensively in Jiangsu Province of China. Symptoms of this kind of disease on panicles are diminished chaff, and badly matched hook inside and outside husk, which result in split hulls and lightened grains. At the mature stage, these panicles erect because of decreased grain weight. Thus, it is often referred to as ‘erect panicle with shrunk-grain’, and is defined as ‘the shrunk-grain panicle’ in this study. Since the grain is abnormal and lightened, the rice yield reduced in different degrees and the field output can badly reduce by 50% or even more. Since the year 2000, the number of sites and the total area in north Jiangsu where the shrunk-grain panicle occured has increased. It has resulted in serious yield
losses, decreased incomes of peasant, and farmers’ doubt of the quality of the seeds provided. Furthermore, it may cause disharmony in the society at a rural area. At present, this phenomenon has already called attention of the department of agricultural services. As a kind of recently-appeared disease of rice in paddy field, the shrunk-grain panicle phenomenon has not been reported overseas. Although there are only a few domestic observation reports, these do not lead to systemic and general description (Zhang ef al. 2002; Chen et al. 2003; Wang et al. 2004, 2005). Concerning the shrunk-grain panicle phenomenon, we still know only little about the changes that have happened to the panicles and grains, and we have no clear standard for distinguishing and determining the nature of its symptom. This situation has blocked the study of the shrunk-grain panicle phenomenon. In this research, we have carried out more systemic and general observation on the
This paper is translaLed from its Chinese version in Scientiu Agriculruru Sinicu ZHANG Zu-jian. Ph D. Tel: +86-514-7972133. Mobile: 13338867606, E-mail: [email protected]. [email protected]
02008.CAAS. All rights reserved. Published by Elsevier Ltd.
Symptom of the Shrunk-Grain Panicle and the Change Characteristics in Its Grain
shrunk-grain panicle by sampling from several sites and analyzed the characteristics of the shrunk-grain panicle, the configuration character of the grain, and the grain weight. It will provide the foundation for further research on the causes and preventive measures of the shrunk-grain panicle.
11
grains in the image were measured using Image Pro Plus, an image analyzing system. Distribution of the grain weight The weight of each single grain was measured separately, with a repetition of 200.
RESULTS
MATERIALS AND METHODS Tested cuIt ivars General variety of japonica rice Wuyujing 3,99-15 were used as tested cultivars.
Time and spot for sampling Continuous investigations on rice plant from milky ripe stage to maturity stage were carried out at several farms (Shanghai, Fangqiang, Dazhong, Baimahu, Gangfu, etc.) in the northern area of Jiangsu Province, China, in 2001, 2002. and 2003.
Sampling methods and contents Shrunk-grain panicles were sampled from farmlands where typical symptoms were found. At the same time, normal panicles were sampled for comparison. When typical shrunk-grain panicles were sampled, some seminormal panicles were sampled simultaneously to investigate the influence of the degree of symptoms on panicles. The main sampling sites included Yangzhou University experimental farm, Fangqiang farm in Yancheng, Baimahu farm in Huai’an, Agriculture Science Center of Lianyungang, etc., China.
Inquisition of panicle properties The panicle length and the number of grains per panicle were measured.
Measure of grain characters Distribution of the grain length and width The length and width of grains were measured using the imagescanning method. Grain samples (over 150 grains) were scanned to image, and then the length and width of the
The occurrence and the symptom of the shrunkgrain panicle Based on the inquisition from 2001 to 2003, it was clear that the occurrence of shrunk-grain panicles almost spread over all planting regions in the north and middle of Jiangsu, and that the repetition of incidence of this disease over years was less. The disease occurred in almost all japonica rice cultivars planted. Observation and comparison among sites in Shanghai farms in 2002 indicated that the Yanjing 9714 and all of 11 japonica rice cultivars caught the shrunk-grain panicle disease. The frequency of this disease differed among cultivars, ranging from 10 to 80%. In addition, investigation in Yangzhou, Huai’an, Yancheng, and Lianyungang showed that the shrunk-grain panicle disease was found in almost all late-growthjaponica rice cultivars as Wuyunjing 3, Wuxiangjing 9, Wuxiangjing 11, Wuxiangjing 14, Wuyunjing 7, Zhendao 88 and Zhendao 99, Huajing 1, Hanfeng 9, 99-15 and Guangling Xiangjing, etc., except for Sidao 10 which had smooth leaf and chaff. Further investigation is still required for protecting rice cultivars from the shrunk-grain panicle disease. Symptoms of shrunk-grain panicles When compared with the normal panicles in the mature stage, grains on shrunk-grain panicles were small, and the grain number was less. Fig.1-1 shows several different panicle samples of Wuyujing 3 with different degrees of the shrunk-grain panicle disease. Generally, the disease occurred at the top of the panicle first and made the grain appearance abnormal (Fig. 1-2). It was also found that the upper part of some diseased panicles was abnormal while the lower part appeared normal. Fig.1-3, 4 represents the shrunk-grain panicles of another cultivar 99-15. Similar to Wuyujing 3, the grains on shrunkgrain panicles diminished obviously and some diminished seriously with the splitting chaffs. Based on the degree of symptoms, the shrunk-grain panicle disease can be divided into three grades: (1) Mild case of shrunk-
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ZHANG Zu-jian er al.
Fig. 1 The appearance of shrunk-grain panicle in japonica rice. 1, the panicle of shrunk-grain panicle with different abnormity extent in Wuyujing 3; 2, the shape of shrunk-grain panicle in Wuyujing 3 at top of panicle; 3, the shape of shrunk-grain panicle in 99-15 at top of panicle; 4, the shape of normal panicle and of shrunk-grain panicle in 99-15; 5, the grain of shrunk-grain panicle in Wuyujing 3; 6, the milled rice of shrunk-grain panicle in Wuyujing 3.
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SvmDtom of the Shrunk-Grain Panicle and the Change Characteristics in Its Grain
grain panicles. Only a few grains on the top part of the panicle were shrunk and split, and the panicle length and the grain number per panicle were about 90% of the normal ones. (2) Medium case of shrunk-grain panicles. There were more shrunk and split grains on the upper part of the panicle, but the grains on the lower part of the panicle were more natural grains. The panicle length and grain number declined to 70430% of the normal ones, and the phenomenon was seen clearly. (3) Serious case of shrunk-grain panicles. Shrunk and split grains were spread all over the panicle. The panicle length and grain number decreased to less than 70% of the normal ones. These abnormal panicles could be seen easily in fields. As seen in the following images, the three different cases of abnormal panicles are very obvious. Table 1 shows the comparison of the normal and the diseased panicles in length and the grain number per panicle, in Wuyujing 3. In the normal panicle, the average length was 14.66 cm and the grain number per panicle was about 98. There was no significant difference between the normal panicles and the mild case of shrunk-grain panicles. In the medium case of shrunkgrain panicles, the length of the panicles decreased by 11.7% and the number of grains decreased by about 19.6%. In the serious case, the panicle length and the grain number per panicle were about 69.6 and 60.4% of the normal ones, respectively. Table 1 Differing characteristics of the shrunk-main Danicle') Category Normal panicle Low shrunk-grain panicle Middle shrunk-grain panicle High shrunk-grain panicle 1)
Length of panicle (cm) Spikelets per panicle 14.66 a 98.2 a 95.1 a 14.33 a 12.94 h 79.0 b 59.3 c 10.20 c
Significant degree at 0.05 by LSD.
The appearance of shrunk-grain panicle Fig. 1-5 shows the comparison of appearance between normal grains and shrunk-grains. It was clear that in addition to the shrunk size of grain, there were grave clefts on chaffs of shrunk grains. This kind of cleft was hypostatic, dissimilar to the ones that were caused by excessive filling in the later mature period, since shrunkgrain panicle was more grave and obvious. Moreover, the color of rice inside the split chaff was usually changed and was easy to distinguish. The more serious the shrunk-grain panicle disease, the more obvious was the grain shrunk and split. Besides, several shrunk grains had abnormal appearance in different degrees. Fig. 1-6 shows the difference of brown rice between
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the normal and shrunk grains. The brown rice inside shrunk grains were small and abnormal, in gray or brown colors, which distinguished them from smooth, transparent normal ones. Population appearance of the shrunk-grain panicles The population appearance of the shrunkgrain panicles in paddy field has some difference according to disease degrees. When compared to the panicle layer of the normal rice plant which looks orderly and heavy, the shrunk-grain panicles of diseased rice plant in paddy field looks disorderly, light and small, so shrunk-grain panicles in severe disease paddy field could be easily seen by naked eyes. By observing the seriously-diseased population, it was clear that the same stub and the same hill have the same disease. Namely, panicles in the same hill were highly correlated. Thus, in paddy fields, the shrunk-grain panicle disease usually occurred irregularly and unevenly. In the hills where the disease was serious, there were slight differences among panicles within the same hill, but in lightly-diseased hills, the degree of disease differed among panicles, and thus, some panicles may be normal, while others be very abnormal.
Distribution of grain shape indices Distribution of normal grain shape indices Fig.2 shows the distribution curve of the length and width of normal grains of Wuyujing 3 planted in Yangzhou University agricultural experimental farm. It was clear that both distributions of the grain length and width showed to be single peaked curves with distinct right skew, which were different to mormal distribution. Hence, we can conclude that under the normal growth condition, the length and width of the grains have regular distribution. Distribution of shrunk grain Fig.3 shows the distribution curves of the appearance of the shrunk grains grown in three different regions in Jiangsu Province with mixed samples. When compared with the single peaked regular distribution of the normal grains, the distribution of the length and width of shrunk grains from all three regions were dispersed, bimodal curves. That is to say, there was a higher distribution center and a lower distribution center on each distribution curve of shrunk grains for one sample, caused by two classes of grains each sample, one was seriously diseased grains, and the other was relatively normal ones. 02008, CAAS. All rightsreserved Publishedby Elsevier Ltd.
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Comparative analysis of the shape and weight for shrunk grains
Fig. 2 The frequency distribution of the shape of the normal grain in Wuyujing 3.
To further find the emerged characters for symptom of shrunk grains, the subnormal grains (the least disease degree) were analyzed, and the results in Fig.4 shows that the distribution of lightly-diseased grains had similar bimodal curves, but the peak that represents normal grains was considerably higher, and on the contrary, abnormal grains were relatively fewer.
Distributionfor weight of shrunk grains Fig.5 shows the distribution for the grain weight of 2 normal grain samples and 3 shrunk grain samples of Wuyujing 3, harvested from different sites. Similar to the frequency distribution for the grain shapes, the distribution curves for grain weight of normal grains were typically single peaked, distinct right skewed and continuous, whereas for shrunk grains, the curves were nearly double peaked. In the mild case of shrunk grain panicles, the proportion of abnormal grains was little. It was clear that the proportion of the distribution in the two kinds of peaks was closely related to the degree of shrunk-grain disease, especially for the peak that represented the abnormal grains. The higher the degree of the disease, the larger were the peak value and the cumulative distribution.
Table 2 shows the average value and coefficient of variation of the normal and shrunk grains. It can be seen that, for normal panicle of japonica rice Wuyujing 3, which was grown in Yangzhou University, the grain weight was about 0.027 g/grain, with a coefficient of variation (CV) of 6-8% for the weight and 4% for the width and length. When compared with the normal grains, the length and width of the shrunk grains decreased with a larger coefficient of variation. The reduction of width and the increment of CV were considerably larger than those observed in the length of the shrunk grains, showing that the reduction of width was the indicator of the shrunk-grain disease. The grain weight was similar to the width. When the shrunkgrain disease occurred, the weight of the grain became lightened, and the irregularity of the grain weight was magnified.
DISCUSSION The history and its present condition of the phenomenonof the shrunk-grain panicle The formal report on the phenomenon of the shrunkgrain panicle was limited in Jiangsu Province of China, and the research on it is still very little (Pan et al. 2002; Zhang 2002a, b; Chen et al. 2003; Fan et al. 2003, 2004; Gu et al. 2003; Wang et al. 2002, 2003, 2004, 2005; Zhang 2005; Lianyungan Seed Station 2002). In fact, as early as in 1966, there was a report on the raised head panicle in Nongken 58 in Zhenjiang, Jiangsu Province (Cui 1966). According to the report, abnormal rice plants had the panicle length reduced, the grains diminished, the chaff split, and the rice was small with color changes. From the phenomenon, it can be seen that it was similar to the shrunk-grain panicle described in the present article. But at that time, the misuse of water and fertilizer was thought to be the main reason. Besides, although there was no formal report, people in Zhenjiang Academy of Agricultural Sciences once discovered shrunk-grain panicles, which caused the output reduction in a part of the fields. However, no deep investigation and research was done on this issue. In
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SvmDtorn of the Shrunk-Grain Panicle and the Change Characteristics in Its Grain
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Fig. 3 The frequency distribution of shape in shrunk-grain panicle.
Fig. 4 The frequency distribution of shape in the slight shrunk-grain panicle.
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Fig. 5 The distribution of grain weight in the normal grain and shrunk-grain panicle. Table 2 Comparison of the shape and weight of grain in a normal panicle with the shrunk-grain panicle
~,-"... Normal -mains from Yangzhou - Uni.
Tbnr nf mli"
.,=-I.
Grains of shrunk-grain panicle from Fangqiang Grains of shrunk-grain panicle from Baimahu Grains of shrunk-grain panicle from Dazhong
Length Average (mm) 6.31 5.88 5.82 5.73
CV (%) 3.90 6.01 6.11 8.89
the 1990s, shrunk-grain panicles occurred sporadically in some areas in Jiangsu Province, including Zhenjiang, Huai'an, Yancheng cities; however, the area and damage were both extremely small to catch the attention of researchers. Until the recent five years, the phenomenon became worse and occurred in all cultivars of japonica rice in Jiangsu Province, causing
Width Average (mm) 3.30 2.76 2.69 2.64
cv (%) 4.32 11.28 9.15 15.25
Grain weight Average (g) CV (%) 0.0271 8.66 0.0234 15.64 0.0227 11.62 0.0232 19.12
serious reduction of yield. Furthermore, the cause and mechanism of the shrunk-grain panicle have not been clarified yet, and it has been difficult for agriculture technique services and seed management services to judge and prevent the disease. According to our investigation, this disease is usually centralized in the north of Jiangsu Province, in-
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Symptom of the Shrunk-Grain Panicle and the Chanpe Characteristics in Its Grain
cluding Yangzhou, Taizhou, Huai’an, Yanchen, Lianyungang cities, and some regions in Nantong and Xuzhou.
The Chinese name and English name of the shrunk-grain panicle Several agricultural researchers have paid attention to the occurrence of the shrunk-grain panicle. There are also a few reports about people’s attempts to prevent it (Wang et al. 2004,2005; Zhang et al. 2005; Yang et al. 2005). There were various reports regarding the name of this phenomenon. Considering that some informal names have caused inconvenience, a unified and formal name was necessary for in-depth studies about the reasons and measures to prevent it. Currently, some names can be seen, for example, ‘the small panicle’ ‘the head-raising panicle’, ‘shrunk-grain panicle’, ‘shrunk-grain and raising panicle’, and so on. Among these names, ‘small panicle’ can easily confuse people with small panicles with normal morphology. ‘Raising panicle’ can lead to a misunderstanding that the phenomenon was caused by the bad environment, such as high or low temperature, or lack of water (Wang et al. 1995; Zhu et al. 2005). ‘Raise panicle’ can also be easily confused with modern cultivars ‘erect panicle’ (Xu et al. 1996; Zhang et al. 2002). Based on its symptom, we thus define it as ‘shrunk-grain panicle’.
The diagnosis of the shrunk-grainpanicle and the establishment of its criterion We have recognized the morphological characteristics of ‘shrunk-grain panicle’, as mentioned above. The symptom was obvious when the degree of shrunk-grain panicle was severe; the whole panicle length, grain length, and grain width were shortened, and the chaffs were split. As for the distribution of abnormal grains on the panicles, the upper part was more seriously damaged than the lower part. To the whole tiller and community, the panicles were erect because of lightened weight. In the field of the mild case of the disease, the symptom was lighter. There is still no suitable criterion to judge the occurrence of shrunk-grain panicles. For example, split in chaff is an important character in shrunk-grains, but in several japonica rice cultivars, it may happen because of fine growth in the late stage.
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To distinguish the disease, all kinds of characteristics of shrunk-grains must be combined. This research provides detailed descriptions about the distribution for grain length, width, and weight in shrunk-grainpanicles. From the results, it can be seen that similar to the other researches (Kuang et al. 2005), the frequency distribution of normal grains was a single peak curve, but that of the shrunk grains was a double-peak curve. By analyzing the abnormity of the distribution curves, it was found that the weights of most grains in diseased panicles are 70-80% of the normal ones. It suggests that besides the split chaff character, the criteria of the shrunk-grain can be defined as about 80% of the normal grain (for grain length, less than 85% of normal grain; for width, 80%;for grain weight, less than 85%). In addition, although the shrunk-grain panicle disease may also cause reduction of the setting rate and the grain number per panicle, it is difficult to provide quantitative criterion for the large scope of variation.
The possible nosogenesis for the shrunk-grain panicle The problems that must be dealt with include the cause and prevention of the shrunk-grain panicle. Now, there are some reports about the reason of the shrunk-grain panicle. (1) Wireworm. Our research team have the data that there were considerably more wireworms in the diseased grains (The result will be reported later). But several questions still remain to be answered: The wireworm has existed for several years in rice (Duan and Wu 2002), but why has the shrunk-grain panicle disease occurred only in recent two years? For two fields nearby with the same variety and same cultivation, why is one field heavily diseased and the other normal? (2) Pathogen. Some people suggest that it may be a new kind of rice disease caused by germs or virus, but there is no convictive evidence. (3) Deterioration of cultivars. Farmers and agricultural services often have this viewpoint. However, the experiment that the same diseased seeds grew up into normal plants in Hainan Province of China, and the fact that there are obvious differences between plants grown in different areas with the same seeds, showed that it could not be caused by heredity factors. (4)Insecticide and herbicide. Although this point of view has been accepted by several researchers, there has been no direct evidence yet. ( 5 )
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Water deficit. It is thought that in the growing period, especially, the meiosis period, the water shortage can seriously cause shrunk-grain panicles. However, in several fields with heavily-damaged shrunk-grain panicles, water management was well done, revealing that water deficit cannot be the main nosogenesis for this disease. Though the research of the shrunk-grain panicle has been carried out for two years, it is still early to provide an affirmative conclusion on its nosogenesis, and considerable study still needs to be done to solve the shrunkgrain panicle. An in-depth study on the nosogenesis for this disease must be urgently done at present.
Acknowledgements This study was supported by the program of Agricultural Three-Project of Jiangshu Province, China (SX2002-08 1).
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