Efeitos da deficiência hídrica sobre as trocas gasosas, tuberização da raiz e teor foliar de polifenóis em cultivares de batata-doce

Abstract

Sweet potato (Ipomoea batatas) leaves, roots and stems are excellent sources of antioxidant polyphenols, including flavonoids, anthocyanins and phenolic acids. Such compounds act as important cellular antioxidants and are fundamental in the tolerance response of plants to environmental stresses. Thus, this study evaluated the effect of water deficit on the initial tuberization phase of sweetpotato cultivars on physiological, biochemical and leaf phenol metabolism. The experiment was conducted under greenhouse conditions, using the cultivars Canadense and Uruguaiana. After the initial planting and branching period (5 weeks), the stress treatment plants were irrigated with 20% field capacity and the control treatment plants with 100% field capacity for 21 days to coincide with the period of stress imposition with the onset of tuberous root formation. Water deficit resulted in a decrease in biomass in both cultivars, with a 20% decrease in leaf number in Canadense cultivar and 40% in Uruguaiana cultivar and a reduction in tuberous root number of 37.5% in Canadense cultivar and 33% in the cultivar Uruguaiana. In the physiological analyzes, it was found that the stress decreased the water potential of the plants, reaching -0.96 MPa in the Uruguaiana cultivar and -1.12 MPa in the Canadense cultivar at 11 days of stress. There were also reductions in photosynthetic rate, transpiration, stomatal conductance and intercellular carbon dioxide concentration in the two cultivars studied. In stressed plants there was a decrease in relative water content and total chlorophyll content and an increase in malondialdehyde content (22% in Canadense cultivar and 58% in Uruguaiana cultivar). Carotenoids increased only in the Canadense cultivar. The total soluble sugar content in roots and leaves decreased in Canadense cultivar and Uruguaiana cultivar increased only in roots. Finally, it was verified that the stress increased the leaf contents of total phenols, flavonoids and anthocyanins in both cultivars. It was concluded that water stress negatively affected both sweet potato cultivars. However, the reductions observed in biometric and physiological parameters were less pronounced in the Canadense cultivar, and this higher tolerance response may be linked to the higher leaf content of antioxidant polyphenols.