Abstract
Quantitative trait loci (QTLs) controlling low temperature germinability (LTG) in rice were identified using 98 backcross inbred lines (BILs) derived from a cross between a japonica variety Nipponbare and an indica variety Kasalath. Seeds of each BIL were stored at 30°C in a drying machine for 7 months to exclude the effects of seed dormancy. Then the germination rate at 15°C for 4 days was scored to represent the LTG. The LTG of Nipponbare and Kasalath was 17 and 61%, respectively, and that of the BILs ranged from 0 to 100%. Five putative QTLs, qLTG-2, qLTG-4-1, qLTG-4-2, qLTG-5 and qLTG-11, were detected on chromosome 2 (G1327: nearest marker locus), 4 (two regions, C946 and C513), 5 (R830) and chromosome 11 (G1465). In the case of qLTG-2, qLTG-4-1 and qLTG-11, Kasalath alleles increased the LTG, while Nipponbare alleles increased it in the case of qLTG-4-2 and qLTG-5. These QTLs explained 40.7% of the total phenotypic variation in the BC1F9 lines. Using chromosome segment substitution lines (SLs), the existence of qLTG-4-1 and qLTG-11 was confirmed and the effect of the Kasalath allele on qLTG-11 was more pronounced than that on qLTG-4-1. The effect of the Kasalath allele on qLTG-4-2, which suppressed the germination, was temporary and disappeared after 7 to 8 month’s storage, suggesting that the disappearance was due to the breaking of seed dormancy and that qLTG-4-2 might control it. Kasalath allele in the case of qLTG-5 decreased the germination rate when the effect of dormancy was completely removed. Therefore, we concluded that qLTG-5 was involved in LTG but not in seed dormancy.
