Global climatic warming inevitably affects rice production. Nine BC 2 F 4 backcross introgression populations derived from crosses between a japonica variety Chaoyou 1 (CY1) as the recurrent parent (RP) and nine donor parents collected from different countries were screened for heat tolerance (HT) at flowering stage. A total of 124 introgression lines (ILs) were selected based on seed setting rate in single plant under high temperature (38℃). The results showed that: introgression lines (ILs) had better HT than CY1, and the frequency of plants with HT derived from the ILs with donors of japonica was higher than that with donors of indica, demonstrating the potential of using genes from japonica varieties to improve HT of breeding line. Progeny testing of the 124 ILs under heat stress and normal condition revealed a high selection efficiency of 64.5% for HT and 80 ILs had higher SF than RP. The 124 selected ILs presented wide segregations for the tested traits in replicated experiments under stress and normal conditions and allowed us to identify eight promising ILs that had greatly improved HT and higher yield than CY1. HT-tolerant plants selected from three pyramiding populations had an average SF of more than 80%, which was significantly higher than that of RP and the highest pyramiding parent. From them, 106 plants with significantly better HT than pyramiding parent were selected, showing ideal pyramiding effect on HT. Detailed comparisons between the ILs and CY1 for yield perform-1950ances and related traits under heat stress and non-stress conditions provided useful information and better understanding in donor selection, selection efficiency and screening method for HT in the BC breeding process. The selected lines with HT will become valuable materials for gene mining and molecular breeding for improvement of HT by high efficient pyramiding of favorable genes.

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