Genetic variability among cotton genotypes for cold tolerance

Even though planting cotton early in the season is advantageous, the cold sensitivity of cotton seedlings and low germination rates, especially in the areas experiencing low temperatures, are the main obstacle for the early seasonal planting. A total of 106 genotypes from three different species; Gossypium hirsutum L., G. barbadense L., and G. herbaceum L. were screened for cold tolerance using three different approaches. Furthermore, the best screening method to differentiate between the genotypes for cold tolerance, and to predict their field emergence rates was also determined. In detail, optimal germination percentages were measured at 30 °C with the results ranging from 61% to 99%. On the other hand, cold temperature germination rates and emergence percentages ranged from 8% to 82% in paper test and from 8% to 88% (the 7th day after planting) in sand test at 18 °C, and field emergence percentages ranged from 44% to 77% at 28 days after planting. A significant difference between cotton species in terms of their tolerance to cold was observed. That is, G. barbadense genotypes had higher germination rates than the other two species in the three methods used. There was no correlation between optimal germination rates and field emergence percentages. Among cold temperature germination methods, the 18 °C paper test was better in predicting of field emergence percentage, in differentiating between genotypes in terms of their cold tolerance and in determining seed vigor. G. hirsutum cultivars; 8106-2, AYDIN-110, CORINA, DP-388, DPL-50, DPL-5614, NAZILLI-342 and one G. barbadense cultivar, GIZA 70 were more cold tolerant among all the cotton cultivars screened in this study.