Identification and application of major quantitative trait loci for panicle length in rice (Oryza sativa) through single-segment substitution lines

Panicle length (PL), an important yield-related trait, strongly affects yield components, such as grain number, grain density and rice quality. More than 200 panicle length quantitative trait loci (PL QTLs) are identified, but only a small number are applied in rice breeding. In this study, we performed QTL analysis for PL using 42 single-segment substitution lines (SSSLs) derived from nine donors in the genetic background of HJX74. Fourteen QTLs and five heterosis QTLs (HQTLs) for PL were recognised. Three QTLs and four HQTLs acted positively, and the other eleven QTLs and one HQTL acted negatively. By scanning the single heterozygous background region of the F-2 population with large-genetic-effect SSSLs, we mapped PL loci qPL6-2 and qPL7-1 to different locations on chromosomes 6 and 7, respectively, in three consecutive years of independent trials. The genetic effects of these QTLs were further assessed. qPL6-2 demonstrated the most positive additive effect (QTL), whereas qPL7-1 achieved the most positive dominant effect (HQTL) for PL. These results indicated that the pyramiding of PL QTLs might increase grain yield and facilitate the application of the beneficial allele in hybrid rice breeding.