Growth and Physiological Responses of Cotton Genotypes to Controlled Drought Using an Automated Irrigation System

Cotton (Gossypium hirsutum L.) is an economically important crop with mutiple uses as fiber, biofuel, feed, food, and medicine. In this tudy, a breeding line with potential drought tolerance, ‘Q1735-4’, developed  by New Mexico State University from a cross of ‘Acala 1517-99’ and ‘Pima Phy 76’, together with its parents were grown in a greenhouse. The plants were characterized for growth and physiological responses to varying substrate volumetric water contents (θ = volumn of water/volumn of substrate) maintained by using an automated irrigation sysytem with soil moisture sensors. Substrate was maintained for nine weeks at four θ levels, i.e., 0.15, 0.25, 0.35, and 0.45 L·L^-1. The results showed that, as θ decreased, total dry weight (DW), stem diameter, and leaf area were decreased linearly for ‘Pima Phy 76’ and ‘Q1735-4’, but quadratically for ‘Acala 1517-99’. However, the reduction varied among genotypes. As θ decreased from 0.45 to 0.25, total DW of ‘Acala 1517-99’, ‘Pima Phy 76’, and ‘Q1735-4’ was decreased by 59.2%, 55.6% and 15.1%, stem diameter was reduced by  33.4%, 28.1% and 22.1%, leaf area was decreased by 70.9%, 65.8% and 34.7%, and plant height was reduced by 39.2%, 32.5% and 23.7%, respectively. As θ further decreased to 0.15, the growth reduction in ‘Q1735-1’ and ‘Acala 1517-99’ was similar but lower than ‘Pima Phy 76’. In conclusion, the growth and development of the three cotton genotypes were negatively impacted by the reduction of water content in substrate. ‘Q1735-4’ was more tolerant to drought than its parents ‘Acala 1517-99’ and ‘Pima Phy 76’.