Diversidade e promoção de crescimento de plantas por bactérias associadas ao capim pangolão

Abstract

Some grass species are resilient under stressful environmental conditions, such as pangolão grass (Digitaria eriantha cv. Suvernola). One of the possible reasons is the presence of growth-promoting bacteria. Thus, the objective was to evaluate the diversity and the growth promotion potential of the endophytic bacterial community of pangolão grass, from different environments in Pernambuco. Bacteria associated with leaves, stem, root and rhizospheric soil were isolated from the pangolon of the Sertão, Agreste and Zona da Mata mesoregions in Pernambuco - Brazil. The diversity assessment was done initially by phenotypic characterization, followed by genotypic evaluation by BOX-PCR, and sequencing of the 16S rRNA gene. Representatives of the groups formed by the BOX-PCR at 90% similarity were chosen for in vitro evaluation of the promotion mechanisms. of plant growth (biological nitrogen fixation - FBN, AIA synthesis, phosphate solubilization and production of siderophores), as well as by experiments in a greenhouse on corn intended to verify each mechanism separately. FBN was evaluated by cultivation under deficit of N, production of AIA by cultivation under water deficit, solubilization of P and production of siderophores by the supply of low solubility P and Fe, respectively. Pangolao grass had high diversity with 325 isolates phenotypically characterized and 244 strains at 100% similarity by BOX-PCR, with 132 strains sent for sequencing. 118 strains showed 96.84 - 99.9% similarity with some previously described in BLAST and 2 phyla, 4 classes, 7 orders, 13 families and 17 genera were identified: Achromobacter, Agrobacterium, Bacillus, Burkholderia, Curtobacterium, Enterobacter, Herbaspirillum, Kosakonia, Ochrobacterium, Paenibacillus, Pantoea, Pseudomonas, Rhizobium, Serratia, Shinella, Stenotrophomonas and Variovarax. In the in vivo evaluation, the strains in the study were superior to the commercial inoculant in all experiments. Strains of pangolão grass outperformed the commercial inoculant in the experiment of low N availability for all evaluated variables, except for the efficiency related to no inoculation and mineral N. In the experiment under water deficit, the new strains also showed better results for all variables evaluated in relation to the commercial inoculant. In the test performed with a low solubility iron source, there was no difference between the commercial inoculating control and all other treatments for stem diameter, leaf area, dry mass of the aerial part, accumulation of N and P in the aerial part and the relative efficiencies. However, strain 252A collaborated with a higher height and 5227 had the highest dry weight of the root. In the experiment with supply of low solubility phosphorus, there was no difference between the commercial inoculant control and the other treatments for aerial part dry mass, N accumulation in the aerial part and all the relative efficiencies, while six strains showed greater accumulation of P. A diversity of bacteria associated with the pangolon may have promoted its resilience. Although each experiment with corn emphasized one of the growth promotion mechanisms studied in vitro, its results in vivo may not have been obtained due to only one mechanism, but rather by the combination of these and other mechanisms not evaluated.