Using Genotyping-by-Sequencing to Develop Broccoli Markers for Construction of a High-density Linkage Map and to Identify QTL Associated with Heat Tolerance

Heat stress reduces the yield and quality of broccoli heads imposing seasonal and geographic limits to broccoli production. For the most part, the risk of producing broccoli with head defects (uneven beads, bracts in heads, etc.) induced by high temperatures has restricted commercial production in the U.S. to western environments in which temperatures are not usually expected to exceed 25-28°C. Heat tolerant broccoli breeding lines have been developed by the USDA Agricultural Research Service to facilitate year-round broccoli production along the eastern coast of the United States. To dissect the genetic basis of this tolerance of non-optimal, high temperatures, a doubled haploid mapping population (N=156) was developed for QTL mapping. Genotyping-by-sequencing produced 1,435 high-quality SNPs which formed 9 linkage groups. Multiple QTL mapping found four QTL and one epistatic interaction that explained 57.5% of the population variation for heat tolerance. Three markers tightly linked to the significant QTL can be used for marker assisted selection in future breeding efforts using the developed tolerant lines.