Identification of quantitative trait loci for panicle structure and grain filling using a cross between indica- and japonica-type high-yielding rice cultivars

ABSTRACT To enhance the yield potential of rice by breeding, it is important to reveal the genetic factors affecting yield components in high-yielding cultivars. Quantitative trait loci (QTL) analysis for panicle structure and spikelet weight as an index of grain filling was conducted using recombinant inbred lines (RILs) derived from a cross between an indica-dominant high-yielding cultivar, Takanari, and a japonica-dominant high-yielding cultivar, Momiroman in 2012 and 2013 in eastern Japan. The grain-filling ability of Takanari is reported to be better than that of Momiroman. Since grain filling is generally better near the tip of the panicle and decreases as the number of branches from the rachis increases, we classified whole panicles into upper and lower side panicles and spikelets into primary, secondary, and tertiary spikelets according to the number of branches from the rachis. On chromosomes 1, 4, and 6, QTLs regulating the number of spikelets per panicle and panicle structure were detected and were most likely identical to GN1a, SPIKE, and APO1, respectively, which has been previously reported as QTLs regulating the number of spikelets per panicle. Takanari produced much heavier secondary and tertiary spikelets than Momiroman on the lower side panicle. On chromosome 5, novel QTLs regulating spikelet weight were detected. The Takanari allele enhanced secondary and tertiary spikelet weight on the lower side panicle. These results indicate that it may be possible to enhance sink capacity and translocation of source with a combination of novel QTLs detected on chromosome 5 and GN1, APO1, and SPIKE. Graphical abstract Chromosomal locations of quantitative trait loci for secondary spikelet weight on whole panicle and secondary and tertiary spikelet weight on lower side panicle in recombinant inbred lines derived from a cross between Takanari and Momiroman in 2013