Our aims to scan the harmful effects of high temperature stress on vegetative development on cotton varieties registered in our country. The experiment was established in the GAPUTAEM trial area in 2020, with 4 blocks according to the Augmented design. Six standards (Tamcot Spnhix, SJU86, AGC208, STV468, ST474, Carmen) and 88 cotton varieties registered in the national variety list were used as trial material. In this study, relative cell injury rate (RCI) and leaf high temperature stress index values (LHTSI) were investigated. Our investigation results show cell membrane damage (%RCI) varied between 41.81% and 74.84%. While the average of the standards used in the experiment was 68.15%, the overall average was found to be 62.42%. Leaf high temperature stress index (LHTSI) values varied between 0.48 and 1.85, while the LHTSI average of the standards was 0.98, and the overall LHTSI average of the experiment was found to be 1.02. It was determined that there was a wide variation among the genotypes screened for vegetatively high temperature stress. Using LHTSI and RCI features, it has been concluded that it is an important, effective, easy, and applicable selection criterion for screening genotypes regarding tolerance or sensitivity to high temperature stress vegetatively in cotton plants. Applying these two parameters together is recommended to obtain more accurate results. It was determined that only the Teksa415 cotton variety was vegetatively tolerant. Vegetatively, 31 cotton genotypes were found in the medium tolerant group and 62 cotton genotypes in the sensitive group.

The potential of cotton genotypes to form buds, flowers and bolls is not sufficient to achieve cotton seed yield targets. Despite global warming buds, flowers and bolls that mature in cotton plants must be successfully transformed into products. However, this is related to the generative tolerance of the genotype to high temperature. In study aims to scan the negative effects of high temperature stress on the generative development on cotton varieties registered in Turkey in the last 10 years. The experiment was established in the GAP International Agricultural Research and Training Center trial field in 2020, with 4 blocks according to the Augmented design. Six standards (Tamcot Spnhix, SJU86, AGC208, ST468, ST474, Carmen) and 88 cotton varieties registered in Turkey National Variety List were used as trial material. In this study, high temperature pollen vitality stress index (HTPVSI) and high temperature shedding stress index (HTSSI) properties were investigated. According to the results of the experiments we conducted, it was determined that the HTPVSI values ranged between 0.17-1.26, the HTPVSI averages of the standards were 1.17, and the HTPVSI averages of the genotypes were 0.99. It has been determined that HTSSI values vary between 0.30-1.71. It was determined that the mean HTSSI values of the standards were 0.89 and the genotypes were 1.00. It was determined that there was a wide variation among the genotypes screened for generatively high temperature stress. Using HTSSI and HTPVSI features is recommended as a selection criterion since it is an important trait for screening genotypes in terms of tolerance or sensitivity to generative high temperature stress in cotton plants. In our study, the results were not similar to each other in terms of HTPVSI and HTSSI traits, due to the low share of flower shedding after applying HTSP (High Temperature Shock Practice: 96 hours of uninterrupted exposure to high temperature during generative periods) in the shedding rate. When the examined HTSSI and HTPVSI traits were examined together, no cotton genotypes were found to be generatively tolerant. In terms of sensitivity of genotypes to high temperature, 18 cotton genotypes were found in the medium tolerant group and 25 cotton genotypes were found in the sensitive group.