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Plant Temperature for Sterile Alteration of a Temperature-Sensitive Genic Male Sterile Rice, Peiai64S
Available online at www.sciencedirect.com
Agricultural Sciences in China 2007, 6(11): 1283-1290
ScienceDirect
November 2007
Plant Temperature for Sterile Alteration of a Temperature-Sensitive Genic Male Sterile Rice, Peiai64S LU Chum-genl, ZOU Jiang-shi', HU Ning2 and YAO Ke-minz I
Jiangsu Academy of Agricultural Sciences, Nanjing 2 10014, P.R.China University of Information Science and Technology, Nanjing 210044, P.R. China
2 Nanjing
Abstract The forecast of sterile alteration for the temperature-sensitive genic male sterile (TGMS) line in two-line hybrid rice seed production was traditionally based on screen temperature determined by weather station. The article put forward a new approach based on plant temperature, which was more exact and direct than the traditional method. The result of the simulation of the self-seeded setting rate of a widely used TGMS iine, Peiai64S, by several temperature parameters and durations, showed that the fertility was directly affected by the plant temperature at a height of 20 cm or the air temperature around it in three days duration. Using the stem temperature of three days at a height of 20 cm as the simulation parameter, the fertility of Peiai64S had the maximum, minimum and optimum temperatures as 22.8, 21.7 and 22.5"C, respectively, whereas 23.2, 21.5 and 213°C when using the air temperature of three days around the height of 20 cm as the parameter. Such temperature indices can be used to conclude the sterile alteration of TGMS for safeguarding seed production of twoline hybrid rice. The article also established a statistic model to conclude plant temperature by water temperatures at inflow and outflow, and air temperature and cloudage from weather station. Key words: plant temperature, sterile alteration, temperature-sensitive genic male sterile rice (TGMS)
INTRODUCTION Rice temperature-sensitive genic male sterile (TGMS) line showed their sterile alteration along with the temperature change. An exact parameter to indicate sterile alteration was useful not only for breeding and identification of such TGMS, but was also helpful to determine and estimate the sterility security of TGMS, and select suitable methods for safeguarding the sterility of TGMS in two line hybrid rice seed production. Up to date, the forecast of TGMS sterile alteration was only based on the daily average temperature determined by the local weather station (screen temperature at a height ~
of 150 cm in a 25 m x 25 m green plot), and used three days average temperature as the alteration point temperature (ftom sterility transformed to partial fertility, seed set from zero increased to 0.5%) (Lu et al. 2001; Yao et al. 1995). For instance, a TGMS, Peiai64S, set its alteration point temperature to be 23.5-24°C for average temperature with three days duration. When the three days average temperature was higher than the point, Peiai64S will exhibit sterility, otherwise partial fertility (Lu et al. 1999; Zou et al. 2003; Liao and Yuan 2000). However, rice production practices showed that such parameter revealed its shortages in the following points: I . Temperature forecasted by a weather station was the same value within a county (or a city), and it
~
This paper is translated from its Chinese version in Scientia Agriculturu Sinica LU Chuan-gen, Ph D, Fax: c86-25-84432691, E-mail: [email protected], [email protected]
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could not express the difference of microclimate of the individual field. Furthermore, the ground of screen in the weather station was different from rice field. It would cause the difference of temperature (Xie et al. 2001). TI. The sensitivepart of rice to the environmentcondition was lower than the height of screen (Xu and Zhou 1996), which would cause the difference of temperature as well. 111. It was confirmed that when TGMS was attacked by lower temperature weather, water irrigation was useful to increase field or plant temperature for maintaining its sterility (Lii et al. 2004; Zou et al. 2005; Xiao et al. 2000; Xiao and Yuan 1997). However, it is difficult to estimate the increased degree of temperature by such forecasted screen temperature. IV. Seed production practices of two-line hybrid rice showed that under the same lower temperatureweather, individualfield exhibited diversified seed purity for the differencesof microclimate. It is inaccurate to estimate fertility by screen temperature. V . The alteration point temperature for fertility used only the upper point temperature (seed set from 0 to 0.5%) and no scale for lower and optimum points. Also, there has been no report for such item so far. The authors considered that the fertility of TGMS was affected by plant temperature,which was caused by all environmental conditions including air, water, soil, wind, etc. During the fertility sensitive period, for rice TGMS of each seed production field, the damaged degree and the effect of measures against lower temperature must be estimated immediately. If these are estimated only by the pollen fertility even seed set, it will be late for taking measures to avoid such damage of lower temperature. Thus, it is important to establish an effective estimating and adjusting method for safeguarding seed production of two-line hybrid rice. The temperature indices of sterile alteration must include two aspects as parameters of type and value. The parameter type denoted the type of temperature (screen temperature of average or maximum or minimum one, otherwise as plant temperature of stem or leaf). The temperature value will include the upper point (seed set from 0 increased to 0.5%), the optimum (show the highest seed set), and the lower point (seed set returned to zero again) of temperature, which were considered as the three basic temperature points. The present research was aimed to establish such three basic temperature points.
MATERIALS AND METHODS Materials A lower temperature-sensitive genic male sterile line, Peiai64S, which was widely used in two-line hybrid rice breeding, was chosen as plant material, and planted in the experimental farm of Jiangsu Academy of Agricultural Sciences, China (32"02'N, 118'51 'E, 8.9 m above sea level).
Sowing date treatments The plants were sowed on 31 May, 15 and 25 June, and 5 July in 2004, and 25 May, 15 and 30 June, and 10 and 15 July in 2005, with seedling growth duration of 30 days, and transplanted with a density of 16.5 cm x 19.8 cm.
Temperature regulatingtreatments During the fertility-sensitive period of all treatments, the microclimate and plant temperature were regulated by water irrigation. In 2004, each of the three irrigation depths of 5, 10, and 15 cm, with current and stayingwater, was used. Only current water irrigation of 15 cm depth was treated in 2005. Non-water field was set as the check synchronously.
Weather elements measurement From initial to the end of sensitive stage, the temperatures were measured from a height of 150 cm to soil (-10 cm under ground surface), and five heights of 150, 100, 60, 40, and 20 cm in rice canopy using a meteorological monitoring system. The equipment was located at the center of the field. The temperature and humidity were measured with PTWD-2A and PTS-2 equipment, the wind speed was measured with EC-9S, and the radiation with TBQ-2 equipment. All data were collected by TRM-ZS1 auto-system per 10 s.
Temperatureof plant stem During the fertility sensitive stage, the stem tempera-
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Plant Ternoerature for Sterile Alteration of a TemDerature-Sensitive Genic Male Sterile Rice. Peiai64S
ture at a plant height of 20 cm was measured continually per 10 s with an improved needle thermocouple sensor under various types of weather.
Fertility and plant traits investigation At the fertility sensitive stage, the plant and panicle height were determined, and furthermore the distance between the last two leaves. For all the sowing date treatments, their self-fertilized seed setting rate was measured by 30 paper bag insulated panicles.
Meteorologicaldata The corresponding meteorological data were obtained from the weather station of Jurong City (3lo57'N, 119"10'E, 27.1 m above sea level), Jiangsu Province, China. The weather station was near the experimental field with almost a similar weather condition. The data were treated by the system of Excel XP and SAS 6.12.
RESULTS Temperature differences between the rice field and the screen of weather station Table 1 shows the temperature differences between the screen of the weather station and the rice field at the heights of 150, 100, 60, 40, and 20 cm. The four periods in Table 1 are: I , from 20 August to 29 September in 2004 and from 9 August to 30 September in 2005. 11, the earliest lower temperature days, 3 to 5 September in 2004. 111, the earliest lower temperature days, 18 to 20 August in 2005. N , the highest temperature day of 16 August, 2005. Table 1 shows
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that under various weather conditions, the temperatures of rice field at each height were different from the screen one of the weather station. Owing to the difference in the underlay surface and growing plant, the temperature at each canopy height was lower than that of the screen of the weather station in the four periods. For the period I , which represented the various weather conditions, the air temperature at the height of 150 cm showed 0.69"C lower than the screen temperature of the weather station, which was at the same height. At the heights of 100, 60,40, and 20 cm, owing to the energy absorbing and reflecting, the temperature difference was enlarged at the four heights. The average temperature at the heights of 100, 60,40, and 20 cm of period I was significantly lower than screen one by 1.10, 0.83, 1.18, and 1.63"C, respectively. A tendency of larger difference along with the height increase was seen, and the largest was seen at 20 cm.
Fertility sensitive position and its height It was reported that developing panicle was the fertility sensitive part of rice (Xu and Zhou 1996). Thus, panicle height was important for determining the fertility sensitive position and the water depth for irrigation to regulate the temperature of the fertility sensitive part. The preceeding studies proved that the sensitive stage was around the stage of meiosis of pollen mother cells (panicle developing stages IV - VI), and the visible morphological trait was at 2 5 cm distance between the last upper two leaves (DL) (Lu et al. 2001). Fig.1 shows the correlation between the panicle height, length, and the DL. The result 'showed that during the stage, the panicle height from the base was 15.3-21.9 cm with an average value of 18.5 cm, and meanwhile, the panicle length was 9.7-16.8 cm with an average value of 13.2
Table 1 Temperatures at different locations in rice field and their differences when compared to that in weather station I
Tempera-
II
location Screen 150 cm 100 cm
Temperature 24.6 f 5.82 23.91 r 5.82 23.50 f 6.80
Differencell
60 cm
23.17 r 5.94 23.42 r 5.88 22.97 f 5.29
4ocm
20 cm I)
N
111 Difference
0.21
Temperature 22.7 22.32 22.21
0.14 0.31 0.54
22.33 22.18 22.25
Difference
0.69" 1.10"
Temperature 23.0 22.89 22.19
0.83" 1.18" 1.63"
22.86 22.69 22.46
0.11
Difference
0.38 0.49
Temperature 32.0 3 1.05 30.79
0.37 0.52 0.45
30.68 30.21 29.44
1.32 1.79 2.56
0.95 1.21
Temperature difference between screen and various heights in rice field. "Different at P
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A
y = 0 6 5 9 6 ~+ 18.596
30
- B
y
=0
7051x+ 13 236
R2= 0 802", n = 132
h
0
I
-20
-10
0
10
20
Distance between last two leaves (cm)
-20
-10
0
10
20
Distance between last two leaves (em)
Fig. 1 Correlation of distance between the last upper two leaves and panicle height (A) or length (B) of Peiai64S.
cm when the DL was -+_5cm. It indicated that the height of 20 cm was the suitable location for fertility sensitivity. Table 2 shows the correlation coefficients between the self-fertilizedseed setting rate and the air temperature at various plant heights or screen one with a liner, conic, and present model (See the part "Model of fertilitytemperature"). The result showed that the coefficients between the self-fertilized seed setting rate and stem or the air temperature at 20 cm height were the highest and a significant correlation. It was indicated that the height of 20 cm was the location expressing the highest correlation coefficient. The result happened to meet the height of panicle at that time. Thus, 20 cm was taken as the suitable location for expressing the fertility of TGMS.
Fertility sensitive stage Determining the fertility sensitive stage was the base to establish a model of fertility-temperature. The fertility sensitive stage can be determined by the distance between the last two
upper leaves or can be checked by the length of the panicle. However, a method by growth days was popular for its advantage in quantitative analysis (Lu et al. 2001). The method was given a range of growing days, and it will cause difficulty for calculating temperature accumulation (Lu et al. 2001), since it does not consider the growing difference owing to temperature. The article determined not only the initiative date, but also the total days, by effective accumulated temperature >24"C. The method was set as: >24"C effective Initiative days from accumulated temperature heading (Total sensitive days) C10"C.d 15 10-20"C.d 12 10 >20"C*d Fertility-temperature model In the sowing date treatments, by analyzing the relationship between the fertility and temperature, it was found that the fertility showed a rule of recovery-increase-decrease along with temperature decreasing. Thus, the article set the base of the model as:
When the temperature decreased to an upper limit (self-fertilized seed setting rate of 0.5%), the TGMS was regarded as fertility, and at the optimum temperature, it showed the highest fertility. When
the temperature decreased furthermore to a lower limit, the self-fertilized seed setting rate returned to zero. Thus, equation (1) was established as:
Model of fertility-temperature
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Plant Temperature for Sterile Alteration of a Temperature-Sensitive Genic Male Sterile Rice, Peiai64S
T-T, P=P,(-) To-TL
A
T ~ - T) B TH -To
(----
Where, P indicated the self-fertilized seed setting rate, while Po indicated its maximum value. T denoted the averaged temperature of the sensitive stage, and T,, TL indicated the upper and lower limit temperatures when the fertility was zero. To denoted the optimum temperature when the TGMS showed maximum fertility. A and B were undetermined parameters and were > 0. Equation (1) shows the following parameters: The derivative equation: I . When P'= 0, the optimum temperature To was calculated, and the highest self-fertilized seed setting rate, Pmm= Po 11. When T 3 THand T d T,, then P,, = 0 Analysis of temperature indices for sterile
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alterationby the model Table 3 shows the simulation of stem or air temperatures with the self-fertilized seed setting rate by three parameters as average, maximum, and minimum temperatures, with three durations of 1, 3, 5 days, and by 0.1"C of step length for the simulation. The result showed that there were significant correlations between the self-fertilized seed setting rate and the temperatures of 20 cm stem, the air temperature or 150 cm air temperatures with the three temperatures and three durations. It also implied that the effect of average temperature was better than that of the maximum or minimum temperatures, and three days duration was better than one day or five days durations. The result also showed that the stem and air temperatures at 20 cm were better than 150 cm air temperature, and the stem temperature at 20 cm showed the best effect of simulation. Thus, the
Table 2 Correlation of the seed setting rate of Peiai64S and the temperature at different heights in field Item Line model Conic model Present modei Sample num.
20 cm air temDerature -0.410" 0.424" 0.778" 85
20 cm stem temoerature -0.316" 0.318" 0.853" 66
60 cm air temoerature -0.225' 0.240' 0.314" 85
4Ocmair temoerature -0.275' 0.275' 0.503" 85
100 cm air temperature -0.224' 0.238' 0.362" 85
150 cm air temperature -0.200 0.227' 0.369" 85
Screen temperature -0.180 0.208' 0.265' 89
*, '* Significance at P<0.05 and P
Table 3 Simulation of the stem or air temperature with three parameters and three durations Location
20 cm stem temperature
A
One day
Three days
Five days
20 cm air temperaNre
One day
Three days
Five days
150 cm (ck) air temperature
One day
Three days
Five days
Average Maximum Minimum Average Maximum Minimum Average Maximum Minimum Average Maximum Minimum Average Maximum MinimIUD Average Maximum Minimum Average Maximum Minimum Average Maximum Minimum Average Maximum MinimW
1 1 1 1 1 1 1
1 1
1 1 1 1 1 1 1 1 1
1 1 1
1 1 1 1 1 1
B
0.24 0.55 1.12 0.37 0.55 1.33 19.35 0.62 0.63 1.17 1.50 27.27 12.14 0.60 5.02 0.88 0.97 0.56 0.22 0.67 0.55 12.61 0.34 15.56 9.15 0.08 0.31
TL
21.6 27.9 17.0 21.7 28.5 17.0 22.2 28.0 18.7 21.9 26.6 17.8 21.5 26.8 17.7 22.0 26.7 19.1 22.9 29.5 17.7 22.8 28.5 17.5 22.9 27.1 18.7
To
T"
Po
R
n
22.3 28.1 17.7 22.5 28.7 17.5 22.4 28.2 18.9 22.1 26.8 18.0 21.8 27.0 17.9 22.3 26.8 19.3 23.4 29.6 17.9 23.0 28.8 17.8 23.2 28.3 19.0
22.5 28.2 18.5 22.8 28.8 18.1 26.0 28.3 19.0 22.3 27.1 23.0 26.0 27.1 19.1 22.6 26.9 19.4 23.5 29.7
10.82 10.82 10.82 10.82 10.82 10.82 10.82 10.82 10.82 10.82 10.82 10.82 10.82 10.82 10.82 10.82 10.82 10.82 10.82 10.82 10.82 10.82 10.82 10.82 10.82 10.82 10.82
0.755" 0.371" 0.964" 0.853" 0.470" 0.550" 0.586" 0.344" 0.6 10" 0.715" 0.360" 0.659" 0.778" 0.356" 0.684" 0.49 1" 0.408" 0.361" 0.559" 0.280 0.426" 0.594" 0.548" 0.686" 0.504" 0.223 0.623"
68
18.0
26.0 28.9 22.9 26.0 28.4 19.1
68 34 66 66 66 64 64 64 83 83 76 85 85 83 86 86 85 41 41 37 42 42 41 43 43 42
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20
22
24
26
28
30
Averaged teniperature of three days ("c)
20
22
24
26
28
30
Averaged temperature of three days ( y j
Fig. 2 Seed setting rate simulated by stem (A) and air temperature (B) at 20 cm height in field.
stem temperature at 20 cm was selected as the best simulating parameter for the model. Equations (2), (3), and (4) are the statistic models of the self-fertilized seed setting rate simulated with the actual self-fertilized seed setting rate and temperatures of 20 cm stem and air, and 150 cm air. With the self-fertilized seed setting rate of 0.5% as initial (upper limit) and that of zero as the lower limit, and with stem temperature at 20 cm for three days, using equation (2), the upper limit temperature and the lower limit temperature were determined to be 22.8 and 21.7"C, respectively. When compared with the air temperature at 150 cm, these were 1.2 and 1.1"C lower, respectively. With the air temperature at 20 cm for three days, using equation (3), the upper limit temperature and the lower limit temperature were determined to be 23.2 and 21.5"C, respectively. When compared with the air temperature at 150 cm, these were 0.8 and 1.3"C lower, respectively (Fig.2).
Stem and air temperatures at 20 cm Considering the energy exchange and balance, the stem and air temperatures in rice canopy were connected with two energy sources: solar radiant energy and water heat energy. To avoid trouble in actual operation, the article established effective statisticmodels as equations (5) and (6), which included the screen temperature (T,,,), cloudage ( N , from 1 to lo), and the water Only by temperature at inflow (Tin)and outflow (To,J. determining the T.. and To,,,the stem or air temperature at 20 cm could be calculated by screen temperature and cloudage, which were both offered by the local weather station. It was helpful to estimate the damage of lower temperature weather and the effects of the adjusting measures in actual seed production.
(R=0.812**,n=46)
YZOstem = 1 0 . 8 2 (~
(R=0.853**,n=66) yZoair=1 0 . 8 2 (~
( R =0.778**,n = 85)
(R=0.594", n=42)
(2)
(R=0.975**,n=46)
Y4 (3)
(4)
DISCUSSION Peiai64S was a widely used TGMS in two-line hybrid rice breeding. Its fertility was controlled by temperature during its sensitive stage. Its sterility usually fluctuated owing to the frequent fluctuation caused by monsoon,
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Plant Temperature for Sterile Alteration of a Temperature-Sensitive Genic Male Sterile Rice, Peiai64S
which resulted in damage to the seed purity of seed production in China southern rice area (Lu et al. 2001; Yao et al. 1995). The first so-called super hybrid rice in China, Liangyou Peijiu, which was released by the authors' research group, was popularized over 7 million ha, and has been the major planted rice for its largest planting area in China from 2002. However, in the lower reaches of the Yangtze River, in the past five years, there was twice lower temperature weather (daily averaged temperaturelower than 24°C) in August, which was the sterility sensitive period of TGMS, therefore, damage was caused to the seed production of Liangyou Peijiu and other two-line hybrid rice. It was a hidden problem for seed production of two-line hybrid rice. In the seed production practices of Liangyou Peijiu, it was found that when attacked by a lower temperature weather, the seed purity exhibited a large difference even if the TGMS was in the same weather condition, owing to the individual differences at landform and water treatment and so on. Researches showed that the fertility of rice TGMS was affected directly by the plant temperature, which was infected by the microclimate of the field (Hu et al. 2006). When attacked by lower temperature weather, and by irrigating warmer water from river or deep pool, the plant temperature would be increased by 2"C, which was effective for safeguarding the sterility of TGMS (Lu et al. 2004; Zou et al. 2005). So far, the forecast of sterile alteration is only based on the temperature information from the weather station; there is lack of study on field microclimate or plant temperature, and especially no research has focused on the temperature value of plant or air around it. In researches of wheat, some researchers used the plant temperature as the parameter for freeze injury and grain growing speed (Feng et al. 2000; Liu and Dong 1992). The present article puts forward a method to conclude the fertility of TGMS by stem or air temperature at 20 cm height, which takes various factors including microclimate and location of field into account. It is more direct and exact than the traditional method. In rice production, we can use it to estimate any field or representative plot of a large field, and to monitor directly the result of regulation for safeguarding seed production in two-line hybrid rice. The technique is: When attacked by lower temperature weather with
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average temperature lower than 24°C during 5-15 days before TGMS heading, using infrared or thermosensor temperature indicator to determine the plant stem temperature at 20 cm height or air temperature around it at 02:00,08:00, 14:00,20:00 (or only 08:OO and 20:OO) every day. If the average value is lower than the line of 223°C for stem temperature or the air temperature is lower than 23.2"C, it implies that the TGMS will transform the sterility to fertility. For safeguarding the sterility, it is necessary to irrigate by warmer water higher than 25"C, and by depth of 15 cm, until the temperature is higher than the above index. The present article also established a statistic model for stem or air temperature at 20 cm height. By the inflow and outflow water temperatures of any field, and the screen temperature and cloudage from the local weather station, the stem or air temperature at 20 cm height can be concluded. For an application example, if one day, the average temperature and cloudage were 22°C and 9, respectively, and the actual water temperature of the field was 23"C, by eqs. ( 5 ) and (6), the stem or air temperature at 20 cm height was calculated to be 22.55 and 22.74"C, respectively, both of which were lower than the above temperature index. By irrigating warmer water from river, the inflow and outflow water temperature were measured as 26 and 24°C by eqs. ( 5 ) and (6), the stem and air temperatures at 20 cm height were calculated to be 23.74 and 24.23"C, respectively. Since both are higher than the above temperature index, it will be effective for safeguarding the sterility of TGMS.
CONCLUSION The stem and air temperature at 20 cm were better than the other parameters. Using the stem temperature of three days at a height of 20 cm as the simulated parameter, the sterile alteration of Peiai64S had the maximum, minimum, and optimum temperature as 22.8, 21.7, and 22.5"C, respectively, and had 23.2,21.5, and 21.8"C, respectively, while using the air temperature of three days at a height of 20 cm as the parameter. Such temperature indices can be used to conclude the sterile alteration of TGMS for safeguarding seed production of two-line hybrid rice. The article also
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established a statistic model to conclude plant temperature by determining temperatures at the water inflow and outflow, and by air temperature and cloudage offered by weather station.
Acknowledgements The research was supported by the National Natural Science Foundation of China (30370830).
References Feng Y X, He W X, Rao M J, Zhong X L. 2000. Relationship between frost damage and leaf temperature with winter wheat after jointing stage. Acta Agronomica Sinica, 26,707-7 12. (in Chinese) Hu N, Lii C G, Zou J S, Yao K M. 2006. Research on plant temperature of TGMS and its application. Chinese Journal of Ecology, 25,512-516. (in Chinese) Liao F M, Yuan L P. 2000. Study on the fertility expression of photo-thermo-sensitive genic male sterile rice Peiai64S at low temperature. Scientia Agricultura Sinica, 33, 1-9. (in Chinese) Liu R W, Dong Z G. 1992. Effect of leaf temperature on grain milking in wheat. Chinese Journal of Agrometeorology, 13, 1-5. (in Chinese) Lii C G, Zou J S, Yao K M. 2004. Techniques for safeguarding seed production of two-line hybrid rice. Review of China Agricultural Science and Technology, 6(Suppl.), 41-44. (in Chinese) Lu X G, Yao K M, Yuan Q H, Cao B, Mou T M, Huang Z H, Zong X M. 1999. An analysis of fertility of PTGMS rice in
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China. Scientia Agricultura Sinica, 32,6-13. (in Chinese) Lu X G, Yuan Q H, Yao K M, Zong X M. 2001. Ecological Adaptability of Photo-Sensitive Male Sterile Rice. China Meteorology Press, Beijing. (in Chinese) Xiao G Y, Deng X X, Tang L, Tang C D. 2000. Approaches and methods for overcoming male sterility fluctuation of PTGMS lines in rice. Hybrid Rice, 15,4-5. (in Chinese) Xiao G Y, Yuan L P. 1997. Effects of water temperature on male sterility of the thermo-sensitive genic male sterile rice lines under the simulated low air temperature conditions appeared occasionallyin high summer. Chinese Journal of Rice Science, 11,241-244. (in Chinese) Xie J H, Huang P B, Huang P J, Long Z Y, Jiang D X. 2001. Comparison of climatic factors between farming fields and meteorological station in early autumn seed production of two-line hybrid rice. Hybrid Rice, 16, 32-35. (in Chinese) Xu M L, Zhou G Q. 1996. Studies on thermo-sensitive part of Peiai64S relating to its fertility expression. Hybrid Rice, 11, 28-30. (in Chinese) Yao K M, Chu C S, Yang Y X, Sun R L. 1995. A preliminary study of the fertility change mechanism of the photoperiod (temperature period) sensitive genic male sterile rice (PSGMR). Acta Agronomica Sinica, 21,187-197. (in Chinese) Zou J S, Lii C G, Yao K M, Hu N, Xia S J. 2005. Research on theories and techniques of irrigation for safeguarding seed production of two-line hybrid rice. Scientia Agricultura Sinica, 38, 1780-1786. (in Chinese) Zou J S, Yao K M, Deng F P. 2003. Analysis on fertility characteristics of Peiai64S and technology for its safely applying. Acta Agronornica Sinica, 29, 87-92. (in Chinese) (Edited by ZHANG Yi-min)
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Agricultural Sciences in China 2007, 6(11): 1283-1290
ScienceDirect
November 2007
Plant Temperature for Sterile Alteration of a Temperature-Sensitive Genic Male Sterile Rice, Peiai64S LU Chum-genl, ZOU Jiang-shi', HU Ning2 and YAO Ke-minz I
Jiangsu Academy of Agricultural Sciences, Nanjing 2 10014, P.R.China University of Information Science and Technology, Nanjing 210044, P.R. China
2 Nanjing
Abstract The forecast of sterile alteration for the temperature-sensitive genic male sterile (TGMS) line in two-line hybrid rice seed production was traditionally based on screen temperature determined by weather station. The article put forward a new approach based on plant temperature, which was more exact and direct than the traditional method. The result of the simulation of the self-seeded setting rate of a widely used TGMS iine, Peiai64S, by several temperature parameters and durations, showed that the fertility was directly affected by the plant temperature at a height of 20 cm or the air temperature around it in three days duration. Using the stem temperature of three days at a height of 20 cm as the simulation parameter, the fertility of Peiai64S had the maximum, minimum and optimum temperatures as 22.8, 21.7 and 22.5"C, respectively, whereas 23.2, 21.5 and 213°C when using the air temperature of three days around the height of 20 cm as the parameter. Such temperature indices can be used to conclude the sterile alteration of TGMS for safeguarding seed production of twoline hybrid rice. The article also established a statistic model to conclude plant temperature by water temperatures at inflow and outflow, and air temperature and cloudage from weather station. Key words: plant temperature, sterile alteration, temperature-sensitive genic male sterile rice (TGMS)
INTRODUCTION Rice temperature-sensitive genic male sterile (TGMS) line showed their sterile alteration along with the temperature change. An exact parameter to indicate sterile alteration was useful not only for breeding and identification of such TGMS, but was also helpful to determine and estimate the sterility security of TGMS, and select suitable methods for safeguarding the sterility of TGMS in two line hybrid rice seed production. Up to date, the forecast of TGMS sterile alteration was only based on the daily average temperature determined by the local weather station (screen temperature at a height ~
of 150 cm in a 25 m x 25 m green plot), and used three days average temperature as the alteration point temperature (ftom sterility transformed to partial fertility, seed set from zero increased to 0.5%) (Lu et al. 2001; Yao et al. 1995). For instance, a TGMS, Peiai64S, set its alteration point temperature to be 23.5-24°C for average temperature with three days duration. When the three days average temperature was higher than the point, Peiai64S will exhibit sterility, otherwise partial fertility (Lu et al. 1999; Zou et al. 2003; Liao and Yuan 2000). However, rice production practices showed that such parameter revealed its shortages in the following points: I . Temperature forecasted by a weather station was the same value within a county (or a city), and it
~
This paper is translated from its Chinese version in Scientia Agriculturu Sinica LU Chuan-gen, Ph D, Fax: c86-25-84432691, E-mail: [email protected], [email protected]
Q2007. CAAS. All rightsresewed. Publishedby Elsevierltd.
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could not express the difference of microclimate of the individual field. Furthermore, the ground of screen in the weather station was different from rice field. It would cause the difference of temperature (Xie et al. 2001). TI. The sensitivepart of rice to the environmentcondition was lower than the height of screen (Xu and Zhou 1996), which would cause the difference of temperature as well. 111. It was confirmed that when TGMS was attacked by lower temperature weather, water irrigation was useful to increase field or plant temperature for maintaining its sterility (Lii et al. 2004; Zou et al. 2005; Xiao et al. 2000; Xiao and Yuan 1997). However, it is difficult to estimate the increased degree of temperature by such forecasted screen temperature. IV. Seed production practices of two-line hybrid rice showed that under the same lower temperatureweather, individualfield exhibited diversified seed purity for the differencesof microclimate. It is inaccurate to estimate fertility by screen temperature. V . The alteration point temperature for fertility used only the upper point temperature (seed set from 0 to 0.5%) and no scale for lower and optimum points. Also, there has been no report for such item so far. The authors considered that the fertility of TGMS was affected by plant temperature,which was caused by all environmental conditions including air, water, soil, wind, etc. During the fertility sensitive period, for rice TGMS of each seed production field, the damaged degree and the effect of measures against lower temperature must be estimated immediately. If these are estimated only by the pollen fertility even seed set, it will be late for taking measures to avoid such damage of lower temperature. Thus, it is important to establish an effective estimating and adjusting method for safeguarding seed production of two-line hybrid rice. The temperature indices of sterile alteration must include two aspects as parameters of type and value. The parameter type denoted the type of temperature (screen temperature of average or maximum or minimum one, otherwise as plant temperature of stem or leaf). The temperature value will include the upper point (seed set from 0 increased to 0.5%), the optimum (show the highest seed set), and the lower point (seed set returned to zero again) of temperature, which were considered as the three basic temperature points. The present research was aimed to establish such three basic temperature points.
MATERIALS AND METHODS Materials A lower temperature-sensitive genic male sterile line, Peiai64S, which was widely used in two-line hybrid rice breeding, was chosen as plant material, and planted in the experimental farm of Jiangsu Academy of Agricultural Sciences, China (32"02'N, 118'51 'E, 8.9 m above sea level).
Sowing date treatments The plants were sowed on 31 May, 15 and 25 June, and 5 July in 2004, and 25 May, 15 and 30 June, and 10 and 15 July in 2005, with seedling growth duration of 30 days, and transplanted with a density of 16.5 cm x 19.8 cm.
Temperature regulatingtreatments During the fertility-sensitive period of all treatments, the microclimate and plant temperature were regulated by water irrigation. In 2004, each of the three irrigation depths of 5, 10, and 15 cm, with current and stayingwater, was used. Only current water irrigation of 15 cm depth was treated in 2005. Non-water field was set as the check synchronously.
Weather elements measurement From initial to the end of sensitive stage, the temperatures were measured from a height of 150 cm to soil (-10 cm under ground surface), and five heights of 150, 100, 60, 40, and 20 cm in rice canopy using a meteorological monitoring system. The equipment was located at the center of the field. The temperature and humidity were measured with PTWD-2A and PTS-2 equipment, the wind speed was measured with EC-9S, and the radiation with TBQ-2 equipment. All data were collected by TRM-ZS1 auto-system per 10 s.
Temperatureof plant stem During the fertility sensitive stage, the stem tempera-
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Plant Ternoerature for Sterile Alteration of a TemDerature-Sensitive Genic Male Sterile Rice. Peiai64S
ture at a plant height of 20 cm was measured continually per 10 s with an improved needle thermocouple sensor under various types of weather.
Fertility and plant traits investigation At the fertility sensitive stage, the plant and panicle height were determined, and furthermore the distance between the last two leaves. For all the sowing date treatments, their self-fertilized seed setting rate was measured by 30 paper bag insulated panicles.
Meteorologicaldata The corresponding meteorological data were obtained from the weather station of Jurong City (3lo57'N, 119"10'E, 27.1 m above sea level), Jiangsu Province, China. The weather station was near the experimental field with almost a similar weather condition. The data were treated by the system of Excel XP and SAS 6.12.
RESULTS Temperature differences between the rice field and the screen of weather station Table 1 shows the temperature differences between the screen of the weather station and the rice field at the heights of 150, 100, 60, 40, and 20 cm. The four periods in Table 1 are: I , from 20 August to 29 September in 2004 and from 9 August to 30 September in 2005. 11, the earliest lower temperature days, 3 to 5 September in 2004. 111, the earliest lower temperature days, 18 to 20 August in 2005. N , the highest temperature day of 16 August, 2005. Table 1 shows
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that under various weather conditions, the temperatures of rice field at each height were different from the screen one of the weather station. Owing to the difference in the underlay surface and growing plant, the temperature at each canopy height was lower than that of the screen of the weather station in the four periods. For the period I , which represented the various weather conditions, the air temperature at the height of 150 cm showed 0.69"C lower than the screen temperature of the weather station, which was at the same height. At the heights of 100, 60,40, and 20 cm, owing to the energy absorbing and reflecting, the temperature difference was enlarged at the four heights. The average temperature at the heights of 100, 60,40, and 20 cm of period I was significantly lower than screen one by 1.10, 0.83, 1.18, and 1.63"C, respectively. A tendency of larger difference along with the height increase was seen, and the largest was seen at 20 cm.
Fertility sensitive position and its height It was reported that developing panicle was the fertility sensitive part of rice (Xu and Zhou 1996). Thus, panicle height was important for determining the fertility sensitive position and the water depth for irrigation to regulate the temperature of the fertility sensitive part. The preceeding studies proved that the sensitive stage was around the stage of meiosis of pollen mother cells (panicle developing stages IV - VI), and the visible morphological trait was at 2 5 cm distance between the last upper two leaves (DL) (Lu et al. 2001). Fig.1 shows the correlation between the panicle height, length, and the DL. The result 'showed that during the stage, the panicle height from the base was 15.3-21.9 cm with an average value of 18.5 cm, and meanwhile, the panicle length was 9.7-16.8 cm with an average value of 13.2
Table 1 Temperatures at different locations in rice field and their differences when compared to that in weather station I
Tempera-
II
location Screen 150 cm 100 cm
Temperature 24.6 f 5.82 23.91 r 5.82 23.50 f 6.80
Differencell
60 cm
23.17 r 5.94 23.42 r 5.88 22.97 f 5.29
4ocm
20 cm I)
N
111 Difference
0.21
Temperature 22.7 22.32 22.21
0.14 0.31 0.54
22.33 22.18 22.25
Difference
0.69" 1.10"
Temperature 23.0 22.89 22.19
0.83" 1.18" 1.63"
22.86 22.69 22.46
0.11
Difference
0.38 0.49
Temperature 32.0 3 1.05 30.79
0.37 0.52 0.45
30.68 30.21 29.44
1.32 1.79 2.56
0.95 1.21
Temperature difference between screen and various heights in rice field. "Different at P
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A
y = 0 6 5 9 6 ~+ 18.596
30
- B
y
=0
7051x+ 13 236
R2= 0 802", n = 132
h
0
I
-20
-10
0
10
20
Distance between last two leaves (cm)
-20
-10
0
10
20
Distance between last two leaves (em)
Fig. 1 Correlation of distance between the last upper two leaves and panicle height (A) or length (B) of Peiai64S.
cm when the DL was -+_5cm. It indicated that the height of 20 cm was the suitable location for fertility sensitivity. Table 2 shows the correlation coefficients between the self-fertilizedseed setting rate and the air temperature at various plant heights or screen one with a liner, conic, and present model (See the part "Model of fertilitytemperature"). The result showed that the coefficients between the self-fertilized seed setting rate and stem or the air temperature at 20 cm height were the highest and a significant correlation. It was indicated that the height of 20 cm was the location expressing the highest correlation coefficient. The result happened to meet the height of panicle at that time. Thus, 20 cm was taken as the suitable location for expressing the fertility of TGMS.
Fertility sensitive stage Determining the fertility sensitive stage was the base to establish a model of fertility-temperature. The fertility sensitive stage can be determined by the distance between the last two
upper leaves or can be checked by the length of the panicle. However, a method by growth days was popular for its advantage in quantitative analysis (Lu et al. 2001). The method was given a range of growing days, and it will cause difficulty for calculating temperature accumulation (Lu et al. 2001), since it does not consider the growing difference owing to temperature. The article determined not only the initiative date, but also the total days, by effective accumulated temperature >24"C. The method was set as: >24"C effective Initiative days from accumulated temperature heading (Total sensitive days) C10"C.d 15 10-20"C.d 12 10 >20"C*d Fertility-temperature model In the sowing date treatments, by analyzing the relationship between the fertility and temperature, it was found that the fertility showed a rule of recovery-increase-decrease along with temperature decreasing. Thus, the article set the base of the model as:
When the temperature decreased to an upper limit (self-fertilized seed setting rate of 0.5%), the TGMS was regarded as fertility, and at the optimum temperature, it showed the highest fertility. When
the temperature decreased furthermore to a lower limit, the self-fertilized seed setting rate returned to zero. Thus, equation (1) was established as:
Model of fertility-temperature
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Plant Temperature for Sterile Alteration of a Temperature-Sensitive Genic Male Sterile Rice, Peiai64S
T-T, P=P,(-) To-TL
A
T ~ - T) B TH -To
(----
Where, P indicated the self-fertilized seed setting rate, while Po indicated its maximum value. T denoted the averaged temperature of the sensitive stage, and T,, TL indicated the upper and lower limit temperatures when the fertility was zero. To denoted the optimum temperature when the TGMS showed maximum fertility. A and B were undetermined parameters and were > 0. Equation (1) shows the following parameters: The derivative equation: I . When P'= 0, the optimum temperature To was calculated, and the highest self-fertilized seed setting rate, Pmm= Po 11. When T 3 THand T d T,, then P,, = 0 Analysis of temperature indices for sterile
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alterationby the model Table 3 shows the simulation of stem or air temperatures with the self-fertilized seed setting rate by three parameters as average, maximum, and minimum temperatures, with three durations of 1, 3, 5 days, and by 0.1"C of step length for the simulation. The result showed that there were significant correlations between the self-fertilized seed setting rate and the temperatures of 20 cm stem, the air temperature or 150 cm air temperatures with the three temperatures and three durations. It also implied that the effect of average temperature was better than that of the maximum or minimum temperatures, and three days duration was better than one day or five days durations. The result also showed that the stem and air temperatures at 20 cm were better than 150 cm air temperature, and the stem temperature at 20 cm showed the best effect of simulation. Thus, the
Table 2 Correlation of the seed setting rate of Peiai64S and the temperature at different heights in field Item Line model Conic model Present modei Sample num.
20 cm air temDerature -0.410" 0.424" 0.778" 85
20 cm stem temoerature -0.316" 0.318" 0.853" 66
60 cm air temoerature -0.225' 0.240' 0.314" 85
4Ocmair temoerature -0.275' 0.275' 0.503" 85
100 cm air temperature -0.224' 0.238' 0.362" 85
150 cm air temperature -0.200 0.227' 0.369" 85
Screen temperature -0.180 0.208' 0.265' 89
*, '* Significance at P<0.05 and P
Table 3 Simulation of the stem or air temperature with three parameters and three durations Location
20 cm stem temperature
A
One day
Three days
Five days
20 cm air temperaNre
One day
Three days
Five days
150 cm (ck) air temperature
One day
Three days
Five days
Average Maximum Minimum Average Maximum Minimum Average Maximum Minimum Average Maximum Minimum Average Maximum MinimIUD Average Maximum Minimum Average Maximum Minimum Average Maximum Minimum Average Maximum MinimW
1 1 1 1 1 1 1
1 1
1 1 1 1 1 1 1 1 1
1 1 1
1 1 1 1 1 1
B
0.24 0.55 1.12 0.37 0.55 1.33 19.35 0.62 0.63 1.17 1.50 27.27 12.14 0.60 5.02 0.88 0.97 0.56 0.22 0.67 0.55 12.61 0.34 15.56 9.15 0.08 0.31
TL
21.6 27.9 17.0 21.7 28.5 17.0 22.2 28.0 18.7 21.9 26.6 17.8 21.5 26.8 17.7 22.0 26.7 19.1 22.9 29.5 17.7 22.8 28.5 17.5 22.9 27.1 18.7
To
T"
Po
R
n
22.3 28.1 17.7 22.5 28.7 17.5 22.4 28.2 18.9 22.1 26.8 18.0 21.8 27.0 17.9 22.3 26.8 19.3 23.4 29.6 17.9 23.0 28.8 17.8 23.2 28.3 19.0
22.5 28.2 18.5 22.8 28.8 18.1 26.0 28.3 19.0 22.3 27.1 23.0 26.0 27.1 19.1 22.6 26.9 19.4 23.5 29.7
10.82 10.82 10.82 10.82 10.82 10.82 10.82 10.82 10.82 10.82 10.82 10.82 10.82 10.82 10.82 10.82 10.82 10.82 10.82 10.82 10.82 10.82 10.82 10.82 10.82 10.82 10.82
0.755" 0.371" 0.964" 0.853" 0.470" 0.550" 0.586" 0.344" 0.6 10" 0.715" 0.360" 0.659" 0.778" 0.356" 0.684" 0.49 1" 0.408" 0.361" 0.559" 0.280 0.426" 0.594" 0.548" 0.686" 0.504" 0.223 0.623"
68
18.0
26.0 28.9 22.9 26.0 28.4 19.1
68 34 66 66 66 64 64 64 83 83 76 85 85 83 86 86 85 41 41 37 42 42 41 43 43 42
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20
22
24
26
28
30
Averaged teniperature of three days ("c)
20
22
24
26
28
30
Averaged temperature of three days ( y j
Fig. 2 Seed setting rate simulated by stem (A) and air temperature (B) at 20 cm height in field.
stem temperature at 20 cm was selected as the best simulating parameter for the model. Equations (2), (3), and (4) are the statistic models of the self-fertilized seed setting rate simulated with the actual self-fertilized seed setting rate and temperatures of 20 cm stem and air, and 150 cm air. With the self-fertilized seed setting rate of 0.5% as initial (upper limit) and that of zero as the lower limit, and with stem temperature at 20 cm for three days, using equation (2), the upper limit temperature and the lower limit temperature were determined to be 22.8 and 21.7"C, respectively. When compared with the air temperature at 150 cm, these were 1.2 and 1.1"C lower, respectively. With the air temperature at 20 cm for three days, using equation (3), the upper limit temperature and the lower limit temperature were determined to be 23.2 and 21.5"C, respectively. When compared with the air temperature at 150 cm, these were 0.8 and 1.3"C lower, respectively (Fig.2).
Stem and air temperatures at 20 cm Considering the energy exchange and balance, the stem and air temperatures in rice canopy were connected with two energy sources: solar radiant energy and water heat energy. To avoid trouble in actual operation, the article established effective statisticmodels as equations (5) and (6), which included the screen temperature (T,,,), cloudage ( N , from 1 to lo), and the water Only by temperature at inflow (Tin)and outflow (To,J. determining the T.. and To,,,the stem or air temperature at 20 cm could be calculated by screen temperature and cloudage, which were both offered by the local weather station. It was helpful to estimate the damage of lower temperature weather and the effects of the adjusting measures in actual seed production.
(R=0.812**,n=46)
YZOstem = 1 0 . 8 2 (~
(R=0.853**,n=66) yZoair=1 0 . 8 2 (~
( R =0.778**,n = 85)
(R=0.594", n=42)
(2)
(R=0.975**,n=46)
Y4 (3)
(4)
DISCUSSION Peiai64S was a widely used TGMS in two-line hybrid rice breeding. Its fertility was controlled by temperature during its sensitive stage. Its sterility usually fluctuated owing to the frequent fluctuation caused by monsoon,
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Plant Temperature for Sterile Alteration of a Temperature-Sensitive Genic Male Sterile Rice, Peiai64S
which resulted in damage to the seed purity of seed production in China southern rice area (Lu et al. 2001; Yao et al. 1995). The first so-called super hybrid rice in China, Liangyou Peijiu, which was released by the authors' research group, was popularized over 7 million ha, and has been the major planted rice for its largest planting area in China from 2002. However, in the lower reaches of the Yangtze River, in the past five years, there was twice lower temperature weather (daily averaged temperaturelower than 24°C) in August, which was the sterility sensitive period of TGMS, therefore, damage was caused to the seed production of Liangyou Peijiu and other two-line hybrid rice. It was a hidden problem for seed production of two-line hybrid rice. In the seed production practices of Liangyou Peijiu, it was found that when attacked by a lower temperature weather, the seed purity exhibited a large difference even if the TGMS was in the same weather condition, owing to the individual differences at landform and water treatment and so on. Researches showed that the fertility of rice TGMS was affected directly by the plant temperature, which was infected by the microclimate of the field (Hu et al. 2006). When attacked by lower temperature weather, and by irrigating warmer water from river or deep pool, the plant temperature would be increased by 2"C, which was effective for safeguarding the sterility of TGMS (Lu et al. 2004; Zou et al. 2005). So far, the forecast of sterile alteration is only based on the temperature information from the weather station; there is lack of study on field microclimate or plant temperature, and especially no research has focused on the temperature value of plant or air around it. In researches of wheat, some researchers used the plant temperature as the parameter for freeze injury and grain growing speed (Feng et al. 2000; Liu and Dong 1992). The present article puts forward a method to conclude the fertility of TGMS by stem or air temperature at 20 cm height, which takes various factors including microclimate and location of field into account. It is more direct and exact than the traditional method. In rice production, we can use it to estimate any field or representative plot of a large field, and to monitor directly the result of regulation for safeguarding seed production in two-line hybrid rice. The technique is: When attacked by lower temperature weather with
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average temperature lower than 24°C during 5-15 days before TGMS heading, using infrared or thermosensor temperature indicator to determine the plant stem temperature at 20 cm height or air temperature around it at 02:00,08:00, 14:00,20:00 (or only 08:OO and 20:OO) every day. If the average value is lower than the line of 223°C for stem temperature or the air temperature is lower than 23.2"C, it implies that the TGMS will transform the sterility to fertility. For safeguarding the sterility, it is necessary to irrigate by warmer water higher than 25"C, and by depth of 15 cm, until the temperature is higher than the above index. The present article also established a statistic model for stem or air temperature at 20 cm height. By the inflow and outflow water temperatures of any field, and the screen temperature and cloudage from the local weather station, the stem or air temperature at 20 cm height can be concluded. For an application example, if one day, the average temperature and cloudage were 22°C and 9, respectively, and the actual water temperature of the field was 23"C, by eqs. ( 5 ) and (6), the stem or air temperature at 20 cm height was calculated to be 22.55 and 22.74"C, respectively, both of which were lower than the above temperature index. By irrigating warmer water from river, the inflow and outflow water temperature were measured as 26 and 24°C by eqs. ( 5 ) and (6), the stem and air temperatures at 20 cm height were calculated to be 23.74 and 24.23"C, respectively. Since both are higher than the above temperature index, it will be effective for safeguarding the sterility of TGMS.
CONCLUSION The stem and air temperature at 20 cm were better than the other parameters. Using the stem temperature of three days at a height of 20 cm as the simulated parameter, the sterile alteration of Peiai64S had the maximum, minimum, and optimum temperature as 22.8, 21.7, and 22.5"C, respectively, and had 23.2,21.5, and 21.8"C, respectively, while using the air temperature of three days at a height of 20 cm as the parameter. Such temperature indices can be used to conclude the sterile alteration of TGMS for safeguarding seed production of two-line hybrid rice. The article also
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established a statistic model to conclude plant temperature by determining temperatures at the water inflow and outflow, and by air temperature and cloudage offered by weather station.
Acknowledgements The research was supported by the National Natural Science Foundation of China (30370830).
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