Evaluation of heat resistance of hybrid rice restorer lines and combinations

In order to reduce the impact of high temperature stress on rice, it is a priority importance in research to explore resistance of rice varieties to high temperature. Reference to industry standard evaluation index for high temperature issued by the Ministry of Agriculture, high temperature resistance characteristics of newly bred restorer lines and commonly used restorer line 'Chenghui727' were identified in production at the highest temperature of 38℃ and normal temperature treatment in artificially-controlled climatic conditions. Combinations of the restorer lines and varieties were divided into five grades. The heat resistance of different parents and hybrid rice combinations was also analyzed at artificially controlled high temperature and room temperature during flowering period. The results showed that:1) One extremely heat resistant restorer line R4093, 9 heat resistant restorer lines (including high fertility restorer lines such as R1015, R107, etc.), 4 extremely heat resistant varieties (combinations) and 25 heat resistant varieties (combinations), 5 extremely heat-sensitive restorer lines, 12 heat-sensitive varieties (combination) and 6 extremely heat-sensitive varieties (combination) were screened and identified. Among these, seed setting rate of high temperature resistant control N22, restoration line R103, R132 and R642, hybrid rice varieties (combination) 'Chuanyou5727', 'Yixiang2115', 'FanyuanA×R642', 'Zhong64xiangA×Huangzhan', 'Chuannongyouhuazhan', 'Rong18A×R1015', 'Yuxiang6203' and 'Chuanyou5727' were more than 70% in this experiment. Although identified as intermediate materials, these lines (varieties) had high potential for high temperature resistance, as further discussed on the production layout of rice varieties. It was concluded that high temperature resistance grade Ⅰ and grade Ⅱ were better and could be arranged in high temperature prone areas, light high temperature areas and high temperature free zones. Grade Ⅲ was an intermediate type that could be arranged in light high temperature areas and high temperature free zones. The grade Ⅳ and Ⅴ were heat sensitive and extremely heat sensitive. These lines could be arranged in a high temperature free zone to avoid high temperature damage to rice. 2) It was also found that the varieties (combinations) with high temperature resistant father (mother) were not always high temperature resistant, while those with high temperature sensitive father (mother) were not always high temperature sensitive. It was also related to the heat resistance and combining ability of the parents. The combination of parents with good heat resistance and good combining ability was mostly heat resistant, and the combination of the parents with poor heat resistance and poor combining ability was mostly heat sensitive. The results showed that the restorer lines R105, R642, R104 and R727 had better high temperature combining ability, but the combining ability of the restorer lines R107 and R1015 was relatively poor. The high temperature combining abilities of male sterile line Gan73A and Neixiang6A were better, while the high temperature combining abilities of FanyuanA, 606A, 608A and Zhong64xiangA were poor. The combination ability of conventional high quality rice variety 'Gold10' was better. Therefore, in order to breed more heat resistant hybrid rice combinations, screening parents with high heat resistant combining ability was critical.