Fertility Of Male-Sterile Lines Via Outcrossing Of Hybrid Rice Responding To Heat Stresses

Rice is the staple food for more than half of the world’s population and its production in East Asia, Southeast Asia and African countries is of tremendous importance for global food security. The discovery of rice male sterile line which available for seed production was opened the way to hybrid rice. Since the yield and quality of the Seed production is an important factor in hybrid rice cultivation, so it is a critical section in hybrid rice production. Compared to the general agricultural systems, hybrid rice seed production is more complex. Seed production not only based on the proper cultivation of both male and the female parents but also the ability to cooperate with each other, such as synchronous flowering, pollen adequate supply, CMS has good pollination situation, etc.. So the system is more sensitivity to the environment. In previous studies, it has been reported that extreme meteorological conditions such as high temperature severely affected seed production of hybrid rice. Due to global warming, the heat stress has imposed serious restriction on the seed production system of hybrid rice.In order to investigate the sensitivity of hybrid rice seed production for hot weather and their possible causes, a field experiment and a pot trail have been done from 2011 to 2015. The field experiment, from 2011 to 2013, which has been set up in Yancheng City in Jiangsu used 4 seed production combination (Xin-liangyou 223, Xin-liangyouxiang 4, Xin-liangyou 223-gai and Liangyou 6188) as test material, and sowed in different stages to get different natural temperature treatment, researched the out-crossing seed setting rate of different combination in each crop to analyzed the sensitivity of hybrid rice seed production for hot weather. The pot experiment has been set up in Jingzhou in Hubei from 2013 to 2015, used 3 representative male sterile line (Ⅱ-32A, Y58S and Guangzhan 63 S) and a broad compatibility restorer line (9311) as test material, to research the fertility rate, flowering habit, pollination character and physiological parametres of lodicule under 3 temperature gradient (daily average temperature of 26℃,28℃ and 30℃) provided by artificial climate chamber. The main results were as follows.1. The seed setting of hybrid rice male sterile line were much more sensitive to temperature than that of common rice. To ordinary rice varieties, when the daily average temperature ≥30≥ or daily maximum temperature ≥35≥ last more than 3d, the seed setting began to fall. But this research showed that, when the 3d average temperature before and after heading stage increased up to 28.0≥, the out-crossing rate of the female parents began to fall, and when it came to 29.0≥ the out-crossing rate severely reduced.2. There has been great differences of high-temperature sensitivity existed among the varied combinations. The combination Xin-liangyou 223-gai and Liangyou 6188 were most sensitivity to high temperature since their largest decreasing amplitude between different corps reached 88.70% and 88.70% respectively. Combination Xin-liangyouxiang 4 was medium sensitive to high temperature, its largest decreasing amplitude was 26.11%, and combination Xin-liangyou 223 suffered minimal impact, its largest decreasing amplitude was 19.60%.3. The main reason of high temperature reduced the out crossing seed setting of hybrid rice male sterile line was the flowering habit of both male sterile line and restorer line changed in different temperature. To restorer line, flowering was earlier and more concentrated in high temperature. To male sterile line, Thermo sensitive male sterile line showed remarkable higher percentage of glume closed florets but poor performance in flowering time synchronization, resulting in much lower pollinated pollen grains and fertility rate.4. Glume closure in heat sensitive male sterile lines was probably related to the physiological state of lodicule. Correlation analysis revealed that percentage of glume closed florets of Ⅱ-32A and Guangzhan 63 S which change greatly was significantly associated with the soluble sugar content in lodicule. The decline of starch and soluble sugars in lodicule and the high abundance of vascular bundles may be the key reasons of the male sterile lines more sensitive to high temperature.