Adaptive reaction of cotton accessions of G. hirsutum L. and G. barbadense L. species to drought stress

Adaptation, process of the adjustment of a plant to specific environmental conditions, is provided by physiological mechanisms (physiological adaptation), and at population level (species) by mechanisms of genetic variability, heredity and selection (genetic adaptation). Intraspecific and the interspecific physiological assessment of adaptation potential to drought stress was carried out on 267 collection accessions and varieties of a cotton (197 accessions of G. hirsutum L. and 70 of G. barbadense L.). Comparative study of the stress reaction of tested accessions to unfavorable environmental factors was carried out based on stress depression indices of viability of seeds in sucrose solution-imitating drought. As a result of the studies different sensitivity of plants to abiotic stress was determined. The amplitude of the changes of physiological parameter during stress allowed roughly divide cotton accessions within each species into groups by defining different degrees of comparative drought resistance of samples. Analysis of the percentage ratio of high drought resistant accessions within species, revealed differences between G. hirsutum L. and G. barbadense L. For the specie G. hirsutum L. percentage of accessions with high drought resistance was 9.1%, for specie G. barbadense L.-28.6%. G. barbadense L., in our view, is characterized by a greater potential for volatility and acclimatization to the new, unusual conditions, capable of better resisting the adverse effects of drought and has great promise for using in breeding. It was found that because of the stress in drought resistant varieties activation of RNA synthesis, increase of labile and decrease of stable DNA was observed which indicates an increase of the physiological liability and functional activity of the genetic apparatus. In susceptible varieties a reduction in the synthesis of RNA and DNA and displacement of DNA fraction ratio towards the stable were noted