Genetic dissection of harvest index and related traits through genome-wide quantitative trait locus mapping in Brassica napus L.

The harvest index (HI) is the ratio of grain yield to the total biomass and represents the harvestable yield of crops. In Brassica napus, the HI is lower than that of other economically important crops, and limited relevant studies have been carried out regarding this issue. In this study, phenotypic analyses of 11 related traits showed the complexity of HI and the feasibility of cultivating desirable varieties with high HI. Quantitative trait loci (QTL) mapping based on a high-density genetic map identified 160 QTL, 163 epistatic loci pairs for HI and three closely related traits: seed yield (SY), biomass yield (BY) and plant height (PH), including two, five and three major QTL for HI, SY and PH, respectively. The related candidate genes underlying the QTL and epistatic loci with coding region variation were identified and investigated, including BnaA02g14010D, homologous to OsTB1, which functions as a negative regulator for lateral branching, and BnaA02g18890D, homologous to OsGW2, which controls grain width and weight. The complex correlation of HI with related traits, numerous QTL and epistatic loci and the candidate genes identified here provide new insights into the genetic architecture of HI, which might further enhance effective breeding strategies for yield improvement in rapeseed.