Temperature difference between screen and various heights in rice field. \*\* Different at *p*<0.01.

Table 3. Temperatures at different locations in rice field and their difference when compared

rature Difference Tempe-

rature Difference

each height were different from the screen one of the weather station.

Tempe-

Table 3 shows the temperature differences between the screen of weather station and rice field at heights of 150 cm, 100 cm, 60 cm, 40 cm, and 20 cm. The four periods in Table 3 are: I: from 20 August to 29 September in 2004 and from 9 August to 30 September in 2005. II: the earliest lower temperature days, 3 to 5 September in 2004. III: the earliest lower temperature days, 18 to 20 August in 2005. IV: the highest temperature day of 16 August, 2005. Table 3 shows that under various weather conditions, the temperatures of rice field at

insulated panicles.

Tempe-

Location Tempe-

to that in weather station

rature

Difference #

production of TGMS rice if only traditional methods are used. Simulation models of rice Tp established in this chapter and its regulation by environmental factors such as by inflow and outflow temperature of irrigated water, and TA, wind speed, sunshine hours from local weather station have provided a more effective method for seed production of two-line hybrid rice.

### **3. Plant temperature for sterile alteration of a thermo-sensitive genic male sterile rice, Peiai64S**

Rice thermo-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 local weather station (screen temperature at a height of 150 cm in a 25 m × 25 m green plot), and used three days average temperature as the alteration point temperature (from sterility transformed to partial fertility, seed setting rate 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 sterile, otherwise partial fertility (Liao *et al* 2000, Lu *et al* 1999, Zou *et al* 2003). 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 could not express the difference of microclimate of 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). II: The sensitive part of rice to the environment condition was lower than the height of screen (Xu *et al* 1996), which would cause the difference of temperature as well. III: It was confirmed that when TGMS was attacked by lower temperature weather, it was useful of water irrigated to increase field or plant temperature for maintaining its sterility (Lu *et al* 2004, Xiao *et al* 1997, 2000, Zou *et al* 2005). 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 temperature weather, individual field exhibited diversified seed purity for the differences of microclimate. It is inaccurate to estimate fertility by screen temperature. V: The alteration point temperature for fertility used only the upper point temperature (seed setting rate from zero to 0.5%) and no scale for lower and optimum points. Also, there is no research report for such item so far. The author consider that the fertility of TGMS was affected by plant temperature, which was caused by all environmental conditions including air, water, soil, wind and so on. 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.

production of TGMS rice if only traditional methods are used. Simulation models of rice Tp established in this chapter and its regulation by environmental factors such as by inflow and outflow temperature of irrigated water, and TA, wind speed, sunshine hours from local weather station have provided a more effective method for seed production of

**3. Plant temperature for sterile alteration of a thermo-sensitive genic male** 

Rice thermo-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 local weather station (screen temperature at a height of 150 cm in a 25 m × 25 m green plot), and used three days average temperature as the alteration point temperature (from sterility transformed to partial fertility, seed setting rate 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 sterile, otherwise partial fertility (Liao *et al* 2000, Lu *et al* 1999, Zou *et al* 2003). 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 could not express the difference of microclimate of 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). II: The sensitive part of rice to the environment condition was lower than the height of screen (Xu *et al* 1996), which would cause the difference of temperature as well. III: It was confirmed that when TGMS was attacked by lower temperature weather, it was useful of water irrigated to increase field or plant temperature for maintaining its sterility (Lu *et al* 2004, Xiao *et al* 1997, 2000, Zou *et al* 2005). 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 temperature weather, individual field exhibited diversified seed purity for the differences of microclimate. It is inaccurate to estimate fertility by screen temperature. V: The alteration point temperature for fertility used only the upper point temperature (seed setting rate from zero to 0.5%) and no scale for lower and optimum points. Also, there is no research report for such item so far. The author consider that the fertility of TGMS was affected by plant temperature, which was caused by all environmental conditions including air, water, soil, wind and so on. 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

two-line hybrid rice.

**sterile rice, Peiai64S** 

of two-line hybrid rice.

The temperature indices of sterile alteration must include two aspects as parameter of type and scale. 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 scale will include the upper point (seed setting rate from zero increased to 0.5%), the optimum (show highest seed setting rate), and the lower point (seed setting rate returned to zero again) of temperature, which were considered as the three basic temperature points. The present chapter was aimed to establish such three basic temperature points.

A lower thermo-sensitive genic male sterile line, Peiai64S, which was widely used in twoline hybrid rice breeding, was chosen as plant material. During the fertility-sensitive period of all treatments, the microclimate and plant temperature were regulated by irrigated water. Three irrigated depths of 5 cm, 10 cm, and 15 cm, each of these with flowing and staying-water were used. Flowing irrigated water of 15 cm depth was also treated. During the fertility sensitive stage, the stem temperature at plant height of 20 cm was measured continually per 10 s with an improved needle thermocouple sensor under various types of weather. 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.

#### **3.1 Temperature differences between rice field and screen of weather station**

Table 3 shows the temperature differences between the screen of weather station and rice field at heights of 150 cm, 100 cm, 60 cm, 40 cm, and 20 cm. The four periods in Table 3 are: I: from 20 August to 29 September in 2004 and from 9 August to 30 September in 2005. II: the earliest lower temperature days, 3 to 5 September in 2004. III: the earliest lower temperature days, 18 to 20 August in 2005. IV: the highest temperature day of 16 August, 2005. Table 3 shows that under various weather conditions, the temperatures of rice field at each height were different from the screen one of the weather station.

