Identification of chromosome regions for high-temperature tolerance in the japonica rice cultivar 'Genkitsukushi' (Oryza sativa L.)

Degradation of the appearance of rice grains due to high temperatures during ripening is a serious problem being worsened by global warming. QTLs for tolerance to high temperature during ripening must be identified in order to develop new cultivars efficiently. Here, we developed recombinant inbred lines (RILs) from crosses between the high-temperature-tolerant 'Genkitsukushi' and the high-temperature-sensitive 'Tsukushiroman'. The occurrence of white-back grains is significantly lower in 'Genkitsukushi' than in 'Tsukushiroman'. We evaluated their high-temperature tolerance and performed quantitative trait locus (QTL) analysis. A QTL for white-back grains on chromosome (chr.) 6 and a large-effect QTL on chr. 8 were identified in the two-year experiments. The QTL on chr. 8 was close to one we previously detected using RILs derived from 'Chikushi 52' x 'Tsukushiroman'. The results indicate that the QTL on chr. 6 is unique to 'Genkitsukushi' x 'Tsukushiroman', and that on chr. 8 could be identical between 'Genkitsukushi' and 'Chikushi 52'. Backcrossed lines which harbor the QTL region on chr. 8 of 'Genkitsukushi' in the background of 'Tsukushiroman' verified its effects. We also analyzed the marker genotypes near the QTLs on chr. 6 and 8 in relatives of 'Genkitsukushi'. We discuss the interaction between these QTLs and their relationship with high-temperature tolerance.