Estirpes de Bradyrhizobium spp. como atenuadoras de déficit hídrico em amendoim (Arachis hypogaea L.)

Abstract

Drought is one of the main factors responsible for limiting the growth and quality of agricultural production worldwide. The use of bacteria of the genera Bradyrhizobium and Rhizobium capable of infecting leguminous plant roots and stimulating the formation of nodules, and consequently nitrogen fixation, is extremely important to expand the sustainability of agricultural systems, especially in Brazil, providing a reduction in use of nitrogen fertilizers and mitigating the effects of water deficit. Thus, the objective of this work was to evaluate the interaction of Bradyrhizobium spp. with peanut genotypes under water deficit conditions, in greenhouse and field, in order to select the interaction best acclimated to stress. Two experiments were carried out (field and greenhouse), with two peanut genotypes (BRS 421 and BRS 423), four inoculants (ESA 123, SEMIA 6144, 16295 and 16986) for the experiment in the greenhouse and three inoculants for the field experiment (ESA 123, SEMIA 6144 and 16295). The experimental design was completely randomized, with a 2 x 6 x 2 factorial arrangement, with five replications, as follows: two peanut genotypes (cultivars BRS 421 and BRS 423); six levels of nitrogen (N) [(i) without N (control); (ii) with N (2 g of ammonium sulphate/pot); (iii) four inoculants (Semia 6144, ESA 123, 16295 and 16986)]; and two water regimes (with and without stress). Twenty-five days after emergence (DAE), irrigation was suspended for 10 days for plants in the stressed group. Sixty DAE were carried out for agronomic evaluations (plant height, shoot dry mass, root dry mass, number of nodules and nodule mass). In the field, two peanut genotypes (BRS 421 and BRS 423) were used, the experimental design was randomized blocks, with 4 blocks containing 10 treatments, totaling 40 experimental plots. Each experimental plot was composed of 2 lines of 3 meters in length, with spacing between lines of 0.80 m, interval between plots of 1.60 m, and useful plot of 4.8 m2. Three strains of Bradyrhizobium sp. (ESA 123, SEMIA 6144 and 16295), a treatment with nitrogen (100kg of N/ha) and an absolute control (without inoculant and nitrogen).The peanut genotypes inoculated with Bradyrhizobium and cultivated under deficit conditions, in a greenhouse, showed a significant effect on the vegetative growth of plants with bacterial inoculants, highlighting the interactions that most contributed to mitigate the effects of water stress: BRS 421 x SEMIA 6144 and BRS 421 x 16295; BRS 423 x ESA 123 and BRS 423 x 16295. The treatments inoculated with ESA 123, 16295 and nitrogen management favored the increase of photosynthetic pigments in the genotypes during water stress. In the field experiment, considering yield, the BRS 421 genotype established a better interaction with the 16295 strains, for the kg/ha grain yield, while the BRS 423 genotype established a better interaction with the ESA 123 strain. Comparing the final production of the two genotypes, the BRS 421 genotype was the most responsive, contributing to higher grain yield and yield.