Potencial hídrico e capacidade fotossintética em genótipos de cana-de-açúcar e cana-energia sob deficiência hídrica

Abstract

Water deficiency is considered the environmental factor that most limits the productivity of sugarcane. Faced with the possibility of its use in biomass production, some programs have initiated new lines of research to develop sugarcane genotypes with higher fiber content, called energy cane. However, little is known about the adaptive mechanisms that participate in the maintenance of the hydric status of energy cane. A better understanding of these mechanisms may contribute to the differentiation of genotypes with higher adaptive potential to dryland conditions. In this sense, the present work aimed to study in a comparative manner the water potential and the photosynthetic capacity of sugarcane and energy cane under water deficiency. The experiment was developed in a greenhouse, located in the Engineering and Agricultural Sciences Campus of the Federal University of Alagoas. Three genotypes were selected for this study, namely: RB11999, RB0442 and RB92579. Five months after planting, the genotypes were submitted to two hydric regimes: adequate hydric regime (Control, C) and with hydric deficiency (+D). The experimental design was in entirely randomized blocks, in a 3x2 factorial scheme, with three genotypes and two hydric regimes, with six repetitions. Gas exchange, maximum photosystem II photochemical efficiency (Fv/Fm), estimated chlorophyll content via SPAD reading, photosynthetic pigments, relative water content and leaf water potential were evaluated. Throughout the water stress period it was observed that all genotypes showed similar reductions for gas exchange. In relation to leaf water potential (Ψw), under water deficiency the genotypes RB92579 and RB0442 reduced up to -1.80 and -1.84 MPa, respectively, while the genotype RB11999, had the most negative leaf water potential, (-3.38 Mpa) being considered the most affected during the stress period. The water deficiency in the soil caused strong physiological damage in all genotypes studied, highlighting the genotype RB11999, which showed physiological characteristics of greater susceptibility to drought, such as intense reduction of photosynthesis, maximum photochemical efficiency of photosystem II, relative water content in the leaf and leaf water potential.