Mechanism of drought tolerance in cotton-response of cotton cultivars to irrigation in the Texas High Plains

Mechanism of Drought Tolerance in Cotton- Response of Cotton cultivars to Irrigation in the Texas High Plains (2011) Esha Poudel Chair of Advisory Committee: Dr. T.L.Thompson Cotton is the most profitable crop produced in the Texas High Plains but water deficiency is a crucial factor affecting both the yield and fiber quality in the region. Increasing cotton tolerance to water stress will be of even greater importance in the future. We tested the hypothesis that different cotton phenotypes, with okra and normal-leaf morphology, will have similar values for physiological responses related to water stress, such as, stomatal conductance, photosynthetic rate, vapor pressure deficit levels, internal CO2 concentration, and transpiration rate, under varying water availability and that these responses will similarly related to yield. A two year field study was conducted to determine the effects and interactions of irrigation amounts and cultivars on yield and quality of cotton and analyze and identify the physiological traits associated with drought tolerance in Lubbock County, Texas in 2008 and 2009. The experiment consisted of three irrigation amounts and two cultivars in each year. An important objective of the study was to see whether the yield and fiber quality will be independent of the phenotypes and the irrigation treatments. In both the years the yield was significantly different between the phenotypically different cultivars. Yields were also not independent of the irrigation in 2009. Fiber quality parameters showed varying response to irrigation amounts in both years. Stomatal conductance, photosynthetic rate and the internal CO2 concentration increased with increase in irrigation in 2009. The normal leaf phenotype was more responsive to irrigation than the okra leaf cultivar and also achieved higher yield. In both cultivars, stomatal conductance and photosynthesis were positively correlated with water availability. As expected, vapor pressure deficit was negatively correlated with water availability. Because the normal leaf cultivar was more responsive to water availability we reject our hypothesis.