QTL Mapping for Reduced Chlorophyll Degradation Under Heat Stress in Wheat.

Heat stress substantially reduces wheat yields worldwide each year. Identification of QTLs for heat tolerance and introgression of stable QTLs into breeding programs can enhance resilience of local popular varieties. Chlorophyll degradation is among the very first signs of heat damage, resulting in reduced light energy capture and consequently lowering photosynthetic rates. Ability to retain chlorophyll content under heat stress is an important tolerance trait. A doubled haploid population of 187 lines was derived from US hard winter wheat cultivars OK06114 (tolerant) x Wendy (susceptible). This population was phenotyped in two independent growth chamber experiments with three replicates during each run. Heat stress (36/30℃ day/night) was applied starting 10 days after anthesis of the primary tiller. Chlorophyll content was measured at 0, 4, 8, 12, and 16 days following the initiation of the heat treatment. The population was genotyped using Genotyping-By-Sequencing (GBS). SNPs were called using the Tassel-5 Reference-GBS Pipeline. A total of 3,470 SNPs with less than 20% missing values was obtained, assigned to 21 individual chromosomes based on physical locations, and used for construction of chromosome-based linkage maps. One major QTL region was identified on chromosome arm 3BS in both experiments using composite interval mapping. This QTL region was common to chlorophyll percent retention at different stages of heat stress and explained 17.6 to 27.4% of phenotypic variation when averaged across two experiments. QTL regions specific to different stages of heat stress for chlorophyll percent retention, QTL mapping for yield traits and approaches to integrate the findings into ongoing breeding programs will also be discussed.