Genetic distance revealed by genomic single nucleotide polymorphisms and their relationships with harvest index heterotic traits in rapeseed (Brassica napus L.)

Abstract

Identifying and using heterotic loci in breeding programs is crucial for increasing crop yield. In this study, we planted 68 inbred lines and their 132 testcrosses at Wuhan and Xiangyang, China. We performed a phenotypic analysis of nine yield-related traits, including plant height, main inflorescence length, branch number, seeds per silique, effective silique number on the main inflorescence, thousand seed weight, biomass yield per plant, seed yield per plant, and harvest index (HI). Additionally, the mid-parent heterosis (MPH) and better-parent heterosis (BPH) for each trait were evaluated. The genetic distance (GD) calculated using high-throughput single nucleotide polymorphisms (SNPs) showed no correlation with HI heterosis, and the difference in GD in the two groups (H-154 and H-155) was not correlated with the difference in HI heterosis levels. The MPH and BPH of HI were significantly correlated with the MPH and BPH of biomass yield per plant, but not with the other traits. Our results indicate that yield-related traits heterosis, including HI heterosis, are extremely complex. The effectiveness of predicting heteroses with GD based on SNPs may be limited, though the SNPs can be used to instead of older markers for high-throughput and accurate genotyping. Our findings may contribute a better understanding to rapeseed breeding and the natural variations of HI heterosis.