Assessing morphological characteristics of elite cotton lines from different breeding programmes for low temperature and drought tolerance
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Cotton breeders in the United States strive to develop regionspecific genotypes adapted to low temperatures and variable soil moistures during earlyseason planting. Nine elite upland cotton germplasm (Gossypium hirsutum L.) lines, representing public breeding programmes from nine states across the cotton belt, were evaluated for cold and drought stresses during seed germination and seedling growth stages. Lines were subjected to three treatments, such as low temperature wellwatered (22/14C, WW), optimal temperature drought stress (30/22C, DS) and optimal temperature wellwatered (30/22C, WW; control), to examine genotypic variability for cold and drought tolerance. The treatment including drought stress was irrigated at 50% of the control. Shoot and root traits measured at 25days after planting were significantly affected by drought and low temperature, where significant genetic variability among lines was observed for both shoot and root parameters. Response indices were developed to quantify variation in the degree of tolerance among the lines to low temperature and drought. Accordingly, OA33 was identified as the most lowtemperaturetolerant line and Acala 151799 as the most droughttolerant line. Identification of both cold and droughttolerant genotypes suggests existing genotypic variability could provide breeders the opportunity to improve cultivar response to earlyseason drought or cold conditions.
