Fifteen common rice maintainer lines and 26 high-yielding restorer lines were used to evaluate their thermal resistance and fertility during flowering and early grain filling stages. The rice plants were subjected to high temperature stress （39-43 ℃） for 1-15 d from main stem flowering. Based on the heat stress index, they were divided into thermal resistant lines, semi-thermal resistant lines, semi-thermal sensitive lines and thermal sensitive lines. Therefore, the maintainer lines K22B, Bobai B and V20B belonged to thermal resistant lines, whereas 11-32B, Zhongzhe B and Zhong 9B belonged to thermal sensitive lines. For rice restorer lines, Minghui 63 had the highest thermal resistance, followed by R207, P32, P929, and the lowest thermal resistant lines P62-2-2, R8006 and P51. The correlation analysis indicated that the heat stress index was significantly correlated with seed-setting rate and abortive grain rate under heat stress, but not under natural conditions. This indicated that heat stress occurred during flowering and early grain filling stages mainly decreased the seed- setting rate and significantly increased the abortive grain rate in both rice maintainer and restorer lines.
FU Guan-fuSONG JianXIONG JieLIAO Xi-yuanZHANG Xiu-fuWANG XiLE Ming-kaiTAO Long-xing
Ten F1 combinations with their male and female parents were employed to evaluate their heat tolerance during the flowering and early grain filling stages. The rice plants were subjected to heat stress（39 °C–43 °C） for 1–15 d during flowering. Based on the heat stress index, heat tolerance was only observed in the F1 combinations H2（K22A × R207）, H3（Bobai A × R207） and H4（Bobai A × Minghui 63）, whereas the others received above 0.5000 of heat stress index. Both parents of the tolerant combination（heat-tolerant × heat-tolerant） possessed heat tolerance, whereas the susceptible combinations were crossed by heat-tolerant（sterile lines） × heat-susceptible（restorer lines）, heat-susceptible × heat-tolerant, or heat-susceptible × heat-susceptible parents. This result indicated that heat tolerance in rice was controlled by recessive genes. Thus, both parents should possess high temperature tolerance to develop heat-tolerant F1 combinations. Furthermore, the heat stress index of F1 combinations was significantly correlated with the heat stress index of restorer lines but not with the heat stress index of maintainer lines. This result suggested that male parents play a more important role in heat-tolerant combinations than female parents. Therefore, the heat susceptibility of the hybrid rice in China is mainly due to the wide application of low-heat-tolerant restorer lines with high yield in three-line hybrid rice breeding.
FU Guan-fuZHANG Cai-xiaYANG Yong-jieXIONG JieYANG Xue-qinZHANG Xiu-fuJIN Qian-yuTAO Long-xing
