A novel Rice QTL qOPW11 Associated with Panicle Weight Affects Panicle and Plant Architecture

The improvement of rice yield is a crucial global issue, but evaluating yield requires substantial efforts. Rice yield comprises the following indices: panicle number (PN), grain number per panicle (GN), 1000-grain weight, and percentage of ripened grain. To simplify measurements, we analyzed one panicle weight (OPW) as a simplified yield index that integrates GN, grain weight, and percentage of ripened grain, and verified its suitability as a proxy for GN and grain weight in particular.

Quantitative trait locus (QTL) analysis using 190 recombinant inbred lines derived from Koshihikari (large panicle and small grain) and Yamadanishiki (small panicle and large grain), japonica cultivars detected three QTLs on chromosomes 5 (qOPW5), 7 (qOPW7) and 11 (qOPW11). Of these, qOPW5 and qOPW11 were detected over two years. qOPW5 and qOPW7 increased OPW, and qOPW11 decreased it at Yamadanishiki alleles. A chromosome segment substitution line (CSSL) with a genomic segment from Yamadanishiki substituted in the Koshihikari genetic background harboring qOPW5 increased grain weight. qOPW11 had the largest genetic effect of QTLs, which was validated using a CSSL. Substitution mapping using four CSSLs revealed that qOPW11 was located in the range of 1.46 Mb on chromosome 11. The CSSL harboring qOPW11 decreased primary and secondary branch numbers, culm length, and panicle length, and increased PN.

In this study, three QTLs associated with OPW were detected. The CSSL with the novel and largest QTL, qOPW11, differed in some traits associated with both panicle and plant architecture, indicating different functions for the meristem in the vegetative versus the reproductive stages. qOPW5 coincided with an identified QTL for grain width and grain weight, suggesting that qOPW5 was affected by rice grain size. OPW can be considered a useful trait for efficient detection of QTLs associated with rice yield.