Genome-wide association study of heat stress-tolerance traits in spring-type Brassica napus L. under controlled conditions

High temperatures have a detrimental effect on growth, development, and yield of Brassica napus. Even a short period of heat stress can lead to yield losses of 15%–20%. A collection of spring-type accessions available in Germplasm Resources Information Network(GRIN)were used to assess the effect of short periods of high-temperature stress at the early flowering stage of B. napus. Two sets of accessions with three replications per set were grown in a greenhouse at 22/18 °C day/night temperatures. Plants from the second set at the 6-day flowering stage were exposed to heat-stress conditions(maximum temperature up to 35 °C) in a plant growth chamber for five days. The heat-stressed plants were then allowed to recover in a greenhouse. Pollen sterility, sterile/aborted pods, and number of pods on main raceme were recorded for both control(set 1) and heat stressed(set 2) plants.Heat susceptibility indices for all three traits were calculated and an association-mapping study was conducted using 37,539 Single Nucleotide Polymorphisms(SNPs) to identify genomic regions controlling the heat stress traits. A total of 5, 8, and 7 quantitative trait loci(QTL) were associated with pollen sterility, sterile/aborted pods, and number of pods on main raceme, respectively. Together they explained respectively 46.3%, 60.5%, and 60.6% of phenotypic variation. Candidate genes in the QTL regions included genes associated with flowering, male sterility, pollen abortion, embryo abortion reducing pollen development,and pod development.