QTL pyramiding for improving of cold tolerance at fertilization stage in rice.

Vigorous cold tolerance at the fertilization stage (CTF) is a very important characteristic for stable rice production in cold temperature conditions. Because CTF is a quantitatively inherited trait, pyramiding quantitative trait loci (QTLs) using marker-assisted selection (MAS) is effective for improving CTF levels in rice breeding programs. We previously identified three QTLs controlling CTF, qCTF7, qCTF8 and qCTF12, using backcrossed inbred lines derived from a cross between rice cultivar Eikei88223 (vigorous CTF) and Suisei (very weak CTF). However, pyramiding of these QTLs for the application of MAS in practical rice breeding programs have not yet been elucidated. In this study, we examined the effect of pyramiding QTLs for improvement of CTF level using eight possible genotype classes from the 152 F3 population derived from a cross between Eikei88223 and Suisei. Increasing of CTF levels in combinations between qCTF7 and qCTF12 and between qCTF8 and qCTF12 were detected. Furthermore, we compared the haplotype pattern around the QTLs for CTF among the rice cultivars from Hokkaido. These results are useful for improvement of new cultivars with high CTF levels using MAS and identification of genetic resources with the novel QTL(s) for CTF.