QTL Mapping of Heat Tolerance in a Doubled Haploid Population of Broccoli using Genotyping-by-Sequencing

Broccoli is a cool weather vegetable crop with a vernalization requirement to initiate and maintain floral development. Breeding for heat tolerance in broccoli has the potential to both expand viable production areas and extend the growing season.  A doubled haploid (DH) population of broccoli (Brassica oleracea var. italica L.) consisting of 159 individuals segregating for heat tolerance was produced by a cross between heat-tolerant and heat-sensitive breeding lines. The population was evaluated for resistance to heat stress (using a 9 point scale) in three years of field trials in Charleston, SC. Population tolerance scores displayed a continuous distribution with a mean of 3.4 points and a standard deviation of 1.5 points. Genotyping-by-sequencing followed by imputation with FSFHap yielded 2,335 non-redundant informative SNPs for genetic map construction. Composite interval mapping was performed using the qtl package in R. Identified QTL and their implications for marker-assisted selection in future breeding efforts will be discussed.