Aplicação de ácido salicílico e inoculação com Bradyrhizobium mitigam os efeitos da restrição hídrica em cultivares de feijão-caupi

Abstract

Water deficit causes damages at different physiological levels in cowpea plants, especially in semi-arid climate conditions, where droughts are frequent at the beginning of the years, as observed in the Brazilian Northeast. However, the bean plant has several defense mechanisms to overcome the water deficit, which can be expressed by tolerant genotypes or by the application of water deficit attenuators. However, the objective of this study was to evaluate the interaction of foliar fertilization with salicylic acid and the inoculation of Bradyrhizobium on growth, physiological and biochemical parameters of cowpea under conditions of water stress. Four genotypes of cowpea were cultivated in the forest nursery of the municipality of Campina Grande under two irrigation slides: W100 (without stress) and W50 (with stress), with 100% and 50% of the evapotranspiration water replenishment, respectively, monitored with the help of an evaporimeter. Were applied two doses of salicylic acid, without salicylic acid and with salicylic acid, at the concentration of 1.0 mM and finally two forms of inoculation (one with Bradyrhizobium type bacteria in cowpea and one without inoculation). The combination of the four factors (4 GEN x 2 LAM x 2 AS x 2 RY) resulted in 32 treatments, arranged in the randomized block design, with four replicates and experimental plot composed of four plants. During the 25 days of conduction of the experiments the cowpea plants were made the first growth measures and then the application of the salicylic acid, after the period of 11 days the plants were evaluated for the leaf water potential and collected for analysis biochemical analysis, where only the aerial part of the plant was used for biochemical analysis. The application of Bradyrhizobium together with salicylic acid promoted the maintenance of the water status of BRS Marataoã, BRS Aracê and BR 17 Gurguéia genotypes under conditions of water deficit. On the other hand, Bradyrhizobium inoculation favored the maintenance of water status in the cultivar BRS Aracê, while salicylic acid promoted the maintenance of water status in BRS Marataoã and BRS Aracê cultivars. The inoculation of Bradyrhizobium with the application of salicylic acid, under conditions of water deficit, ensured the main maintenance of the absolute growth rate of the cultivars BRS Marataoã and BR 17 Gurguéia, besides the leaf area for BR 17 Gurguéia and of the dry mass for the BRS Marataoã, through increases in proline concentration for both and Superoxide Dismutase activity only for BRS Marataoã. The inoculation of Bradyrhizobium favored the maintenance of the absolute growth rate, foliar area and dry mass of BRS Marataoã and BRS Aracê cultivars, under conditions of water deficit, by increasing proline and ascorbate peroxidase activity in both, besides increased catalase activity in BRS Aracê cultivar. In addition, inoculation promoted the increase of most of the growth parameters in the cultivar BR 17 Gurguéia, due to the increase in proline levels. The application of salicylic acid, under conditions of water deficit, ensured the maintenance of most of the agronomic parameters in all cultivars evaluated. Were part of the mitigation process of the effects of the water deficit on the cultivar BRS Rouxinol, proline and superoxide dismutase; in BRS Marataoã, proline and catalase; and in BRS Arace, proline, ascorbate peroxidase and catalase.