Physiological traits for drought phenotyping in cotton/Tracos fisiologicos para fenotipagem de algodoeiro sob seca

The objective of this study was to identify physiological traits that could distinguish between cotton genotypes that were tolerant or sensitive to water deficits. The experiment was conducted in a completely randomized design through a factorial combination to analyze four genotypes (BRS 187 8H and ACALA SJ-4-water deficit tolerant; CNPA 7H and SU-0450/8909-water deficit sensitive) and two water regimes (watered/always irrigated and stressed/with a water deficit imposed at flowering). Irrigation was suspended for the plants in the water deficit treatment groups when their first flowers appeared. Leaf water potential (ψpd) was monitored until the plants reached -3.0 MPa predawn, at which point leaf samples were collected for analysis. The plants were reirrigated and monitored for a recovery to 50% of leaf water potential. The maximum photochemical efficiency (Fv/Fm), chlorophyll content (SPAD index), relative water content (RWC), disruption of the cell membrane via membrane leakage, carbon isotope composition (δ[sup.13]C), seed cotton yield and fiber quality were evaluated. The trends in membrane leakage and carbon isotope composition were different between the tolerant and sensitive genotypes under a water deficit, which makes these physiological traits suitable for screening for tolerance to water deficits in cotton. Keywords: abiotic stress, Gossypium, water deficit. Objetivou-se identificar variaveis fisiologicas para distinguir genotipos de algodoeiro tolerantes e sensiveis ao deficit hidrico. O experimento foi conduzido no delineamento inteiramente casualizado em arranjo fatorial, sendo testados quatro genotipos (BRS 187 8H e ACALA SJ-4-tolerante ao deficit hidrico; CNPA 7H e SU-0450/8909-sensiveis ao deficit hidrico) e dois regimes hidricos (controle-sempre irrigado e com deficit hidrico imposto na emissao da primeira flor. Na emissao da primeira flor, a irrigacao foi suspensa para o grupo a ser submetido ao deficit hidrico. O potencial hidrico foliar foi monitorado na antemanha ate que as plantas dos cultivares em estudo atingissem -3,0 MPa, ponto no qual coletaram-se amostras foliares para analises fisiologicas. Apos, irrigou-se as plantas ate a obtencao de valor superior a 50% do potencial hidrico foliar (-1,50 MPa). Avaliaram-se a eficiencia fotoquimica maxima (Fv/Fm), o conteudo de clorofila via indice SPAD, o conteudo relativo de agua (CRA), o extravasamento de eletrolitos, a composicao isotopica do carbono ([δ.sup.13]C), o rendimento de algod