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 State, Brazil, between June and December 2015. Treatments were formed from a split-plot arrangement, in which the plots were 6 water deficit periods (P) (P1 = No deficit, P2 = Deficit in the initial growth stage, P3 = Deficit in the flower bud stage, P4 = Deficit in the flower stage, P5 = Deficit in the boll stage and P6 = Deficit in the open boll stage) and the subplots, 2 upland cotton cultivars (C) (C1 = Brazil Seeds 286 and C2 = BRS 336), in randomized block design, with 4 replicates. Water deficits reduced the gas exchange of the upland cotton plants, mainly stomatal conductance, transpiration and photosynthesis. The cotton cultivars BRS 286 and BRS 336 presented similar behavior in the different water deficits applied on different phenological stages. Cotton was less tolerant to water deficits in the boll formation stage and more tolerant in the initial growth and flower bud stages.
Key words: Gossypium hirsutum L. r. latifolium H., water stress, physiology.
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