Determination of DNA markers associated with tolerance/resistance to high temperature stress in cotton (Gossypium hirsutum L.)

94 cotton (Gossypium hirsutum L.) genotypes from domestic and foreign sources, especially cotton varieties originating from our country and registered cotton varieties, were placed in a low tunnel for 96 hours uninterruptedly during the peak flowering period in this study. By using phenotypic and genotypic parameters before and after stress, SNPs obtained by genotyping by sequencing (GBS) in cotton and identification of high temperature stress tolerance markers by association mapping method and enabling marker-assisted selection in terms of tolerance to high temperature stress were investigated. The study was carried out in 4 blocks according to the augmented trial design in the GAPUTAEM trial area in the 2020 cotton production season. During the flowering period, all blocks were placed in a low tunnel in pairs on the same day for 4 days, and a High Temperature Shock Application (YSŞU) was created. In the research, 5 parameters, including Relative Cell Injury (RCI) (%), Leaf Temperature (YS) (°C), Leaf SPAD value (YSPAD), Shedding Rate (SO) (%) and Pollen Viability (PC) (%) parameters, before and after stress, were examined in terms of phenotypic. In addition, using these phenotypic data, association analyses were performed among 6670 (MAF<0.05) strong SNP markers obtained by the GBS method. As a result of evaluating the phenotypic observations taken before and after the High Temperature Shock, RCI were determined. 51 cotton genotypes are Sensitive in terms of RCI values; 30 cotton genotypes were in the Medium Tolerant group and 13 cotton genotypes were in the Tolerant group. In terms of YS index, 39 cotton genotypes were found to be in the Sensitive class, 52 cotton genotypes in the Medium Tolerant class, and 3 cotton genotypes in the Tolerant class. In terms of YSPAD values, it was determined that 38 cotton genotypes were in the Sensitive group, 54 cotton genotypes were in the Medium Tolerant group and 2 cotton genotypes were in the Tolerant group. As a result of the evaluation applied in terms of the SO, it was determined that 40 cotton genotypes were in the Sensitive group, 51 cotton genotypes were in the Medium Tolerant group and 3 cotton genotypes were in the Tolerant group. When the index values in terms of PC were examined, it was determined that 54 cotton genotypes were in the Sensitive group, 36 cotton genotypes were in the Medium Tolerant group and 4 cotton genotypes were in the Tolerant group. As a result of association mapping, 149 quantitative trait loci (QTL) were detected in 26 different chromosomes of cotton by general linear model (GLM) and mixed linear model (MLM) methods. According to the GLM and MLM methods related to resistance/tolerance to high temperatures regarding the RCI examined, it was determined that there were 23 SNP markers in different chromosomes of cotton, and 2 of these markers were found to be highly significant according to -Log10(P-Value)>2.5 by both methods. 36 markers were detected in different chromosomes related to high temperature resistance/tolerance regarding YS, and 10 markers were found to be very important according to the probability of -Log10(P-Value)>2.5' by both methods. According to GLM and MLM methods, 27 markers were identified in different chromosomes related to high temperature resistance/tolerance regarding YSPAD values, and 6 markers were found to be very important according to the probability of -Log10(P-Value)>2.5 by both methods. Regarding the SO values, 20 markers were determined in different chromosomes by both methods related to resistance/tolerance to high temperatures, and 3 markers were found to be very important according to -Log10(P-Value)>2.5 by both methods. According to the GLM and MLM methods related to high temperature resistance/tolerance regarding PC values, 10 markers were determined in different chromosomes of cotton, and 3 of these markers were found to be very important according to the probability of -Log10(P-Value)>2.5 by both methods. As a result of this research, once the SNP markers with high confidence values and the accuracy of the detected gene matches are confirmed in different studies, marker-assisted selection (MAS) for high temperature resistance/tolerance will be possible. In addition, cotton genotypes determined to be tolerant based on the traits examined in the study related to high temperature resistance/tolerance will shed light on high temperature stress breeding studies.