QTLs and Potential Candidate Genes for Heat Stress Tolerance Identified from the Mapping Populations Specifically Segregating for F(v)/F(m) in Wheat.

Despite the fact that F(v)/F(m) (maximum quantum efficiency of photosystem II) is the most widely used parameter for a rapid non-destructive measure of stress detection in plants, there are barely any studies on the genetic understanding of this trait under heat stress. Our aim was to identify quantitative trait locus (QTL) and the potential candidate genes linked to F(v)/F(m) for improved photosynthesis under heat stress in wheat (Triticum aestivum L.). Three bi-parental F(2) mapping populations were generated by crossing three heat tolerant male parents (origin: Afghanistan and Pakistan) selected for high F(v)/F(m) with a common heat susceptible female parent (origin: Germany) selected for lowest F(v)/F(m) out of a pool of 1274 wheat cultivars of diverse geographic origin. Parents together with 140 F(2) individuals in each population were phenotyped by F(v)/F(m) under heat stress (40°C for 3 days) around anthesis. The F(v)/F(m) decreased by 6.3% in the susceptible parent, 1-2.5% in the tolerant parents and intermediately 4-6% in the mapping populations indicating a clear segregation for the trait. The three populations were genotyped with 34,955 DArTseq and 27 simple sequence repeat markers, out of which ca. 1800 polymorphic markers mapped to 27 linkage groups covering all the 21 chromosomes with a total genome length of about 5000 cM. Inclusive composite interval mapping resulted in the identification of one significant and heat-stress driven QTL in each population on day 3 of the heat treatment, two of which were located on chromosome 3B and one on chromosome 1D. These QTLs explained about 13-35% of the phenotypic variation for F(v)/F(m) with an additive effect of 0.002-0.003 with the positive allele for F(v)/F(m) originating from the heat tolerant parents. Approximate physical localization of these three QTLs revealed the presence of 12 potential candidate genes having a direct role in photosynthesis and/or heat tolerance. Besides providing an insight into the genetic control of F(v)/F(m) in the present study, the identified QTLs would be useful in breeding for heat tolerance in wheat.