Screening Elite Cotton Genotype from Different Breeding Programs for Low Temperature and Drought Stress Tolerance.

Since temperature and drought stresses are the two major factors limiting crop performance across the world, cotton breeders strive to develop region- and stress-specific genotypes for a niche environment. We hypothesize that there exists genetic variability among the genotypes developed at different U.S. cotton breeding programs. Nine elite Upland cotton germplasm (Gossypium hirsutum) lines from the Regional Breeders Testing Network (RBTN) supported by Cotton Incorporated (www.cottonrbtn.com) from nine US states were evaluated for cold and drought stresses during seed germination and seedling growth stages. The experiment was conducted in sunlit plant growth chambers known as soil-plant-atmosphere-research (SPAR) units with three replications. The treatments include control (optimum temperature, 30/22°C), low temperature (22/13°C) and drought stress at optimum temperature. The control and low temperature-grown plants were well-watered while the drought stress treatments were irrigated at 50% of the control. After 25 days after seeding, morpho-physiological parameters including root traits using winRHIZO root image analysis system were measured. Genotypes differed for leaf area and root diameter, length and root surface area per unit weight, and time to 50% seed emergence. All measured parameters differed significantly at low temperature compared to the control. All parameters also differed for drought conditions except for root average diameter, root tips, total pigments, and time to 50% emergence. Low temperature sensitivity response index (LTSRI) and drought sensitivity response index (DSRI) were estimated by summing individual response indices calculated as the value of a parameter at stress condition divided by the value for same parameter at optimum condition. Accordingly, cotton genotypes were classified as cold sensitive (3), moderately cold tolerant (2), and cold tolerant (4) based on combined LTSRI. Similarly, genotypes were classified as drought sensitive (5), moderately drought sensitive (2), moderately drought tolerant (1), and drought tolerant (1) based on combined DSRI. Among the nine genotypes tested, OA-33 (Jim Olvey’s program in Arkansas) was the most low-temperature tolerant and Acala 1517-99 (Jinfa Zhang’s program in New Mexico) was the most drought tolerant. The identified cold and drought tolerant genotypes could be used in cotton breeding programs to develop new genotypes for low temperature and drought tolerance.