Identification of quantitative trait loci (QTL) related to heat stress tolerance in Chinese cabbage

A genetic linkage map of Chinese cabbage (Brassica rapa L.) ssp. Pekinensis was constructed with 142 RAPD (random amplified polymorphic DNA) and 24 SSR (simple sequence repeat) markers using F2 population comprising of 91 individuals. The F2 individuals were obtained from F1 that was derived by crossing heat tolerant line 92 and a heat sensitive line 93. To investigate the heat stress response twenty day old seedlings of F3 population were exposed to 43oC for seven days under 80% relative humidity (RH) followed by three days of recovery under normal controlled growth conditions (15 to 22oC). Heat stress response was based on visual ratings (0=survived and 1=dead) after the heat treatment. The segregation of linkage with each marker was examined by using JoinMap version 4.0. Fourteen linkage groups were generated with 101 mapped markers covering 963.7 cM with an average marker interval 9.5 cM. Quantitative trait loci (QTL) were mapped for heat stress tolerance by using MAPQTL 5.0 package. Three QTLs were discovered explaining 17.6%, 18.5% and 41.1% of the total phenotypic variation of heat tolerance. These QTLs linked to heat stress tolerance would be useful in marker assisted selection program for heat stress tolerance breeding of Chinese cabbage.