Gas exchenge in upland cotton cultivars under water deficit strategies.

Upland cotton crop in Brazilian semiarid zones has a favorable factor, the duration of the mean solar day. On the other hand, cotton is frequently subjected to soil water deficit. Several physiological indexes are related to the use of water by plants. Among them, photosynthesis and stomatal conductance stand out, as osmotic adjustment, such as stomatal closure, allows plants to escape dehydration and loss of turgor through the maintenance of the water content in the cells. Therefore, the efficiency of water use for irrigated production systems need to be optimized, especially in the cotton crop, as it is a species of great economic and social importance. Aiming to evaluate the gas exchange of upland cotton cultivars cultivated in the Brazilian semiarid, subject to water deficit periods on the phenological stages, an experiment was carried out at the Campina Grande Federal University, Pombal county campus, Paraíba, between June and December 2015