Development of heat tolerant introgression lines and preliminary quantitative trait loci (QTL) analysis at flowering stage in Oryza sativa L.

The efficacy of modern rice varieties has been challenged by global warming because of their incapability to tolerate heat stress. Breeding for heat tolerance (HT) is therefore essential. Molecular breeding studies on HT in hybrid rice is sparse although HT quantitative trait loci (QTL) have been discovered. China is the leading country for hybrid rice production, however, introgression of HT alleles to hybrids is not practiced in breeding programmes. Therefore, the objectives of this study were to introgress HT alleles from indica donors Bg 90-2 and Mengguandamagu to SH 527, a popular parent in hybrid variety development, and to identify the associated DNA markers with HT to facilitate hybrid rice molecular breeding in China. The BC2F2:4 introgression lines were produced by crossing donor and recurrent parents and their performances were evaluated at two provinces of China in 2011 and 2012 under normal and heat stress conditions. The data were subjected to ANOVA and HT was compared against the standard heat-check variety N22. Out of 600 SSR markers, 61 and 59 markers were polymorphic for the two crosses SH 527/ Bg 90 ‒ 2 and SH 527/ Mengguandamagu, respectively and introgression lines were subsequently genotyped. The single-marker analysis was performed to detect marker trait associations. A total of 46 HT introgression lines were obtained with 88.3 % of homozygosity for HT alleles and seven high yielding HT lines were specifically selected for the provinces. Under heat stress, 42 significant marker trait associations were detected. Two of these were previously reported in HT QTLs implying their applicability in rice breeding programmes.