Identification of QTLs with additive, epistatic, and QTL × environment interaction effects for the bolting trait in Brassica rapa L.

Abstract

Bolting is an important agronomic trait in Brassica rapa crops due to its effect on yield and quality. Bolting is a complicated trait regulated by multiple genes that is highly influenced by the environment. Defining the chromosomal region(s) involved and clarifying the genetic interactions is important for improving the effectiveness of marker-assisted selection. Our objectives were to map quantitative trait loci (QTLs) controlling bolting in B. rapa and to study epistasis and QTL × environment interactions. A recombinant inbred line population (RILs, F2:6) derived from a cross between late—(08A061) and early bolting (09A001) lines was used to determine the genetic basis for three bolting indices; bolting index (BI), days to 5-cm-high elongated floral stalk (DE), and flowering time (FT) in four environments (E1–E4). Twenty-three additive QTLs were identified for BI, DE, and FT using single environment phenotypic scores. Phenotypic variation explained by each additive QTL and the total variation ranged from 5.90–33.15 %, and from 19.54–54.87 %, respectively. Eight additive QTLs and six pairs of epistatic QTLs were detected across the four environments. Phenotypic variation explained by the additive and epistatic QTLs ranged from 1.46–17.39 % and 0.70–4.73 %, respectively. Three of eight additive QTLs and zero of six pairs of epistatic QTLs showed environmental interactions. Phenotypic variation explained by each additive QTL × environment ranged from 0.88–2.15 %. Our results will contribute to an understanding of the genetic control of bolting in B. rapa, and enable breeders to determine the appropriate selection strategy with respect to bolting in breeding programs.