Diversidade e eficiência em promoção do crescimento vegetal de bactérias de solos da caatinga pernambucana oriundas de nódulos de leguminosas arbóreas nativa

Abstract

The use of legumes inoculated with competitive and efficient nitrogen-fixing bacteria is a strategy to enhance the practices in the regeneration of degraded areas. In addition to encouraging the establishment of plants, the use of efficient strains reduces the cost of deployment and maintenance of agricultural systems, eliminating the use of nitrogenous fertilizers. But for the success of these practices is necessary to know the diversity of bacteria in the legumes nodules and evaluate their proper efficiency. The objective of this study was to evaluate the diversity and efficiency of bacterial isolates from three native species nodules Caatinga, grown in the State of Pernambuco soils deposited in the Agricultural Interest Collection of Microorganisms of Embrapa Semi -Arid. After certification purity of the stock of bacteria, all 308 isolates passed through a selection of amplicons nodC and nifH genes using a duplex-PCR approach. Among the bacteria evaluated, positive amplification were obtained for 18 isolated from mulungu, 40 to jurema-preta and 44 to angico. All these isolates were evaluated for NaCl tolerance and high temperatures "in vitro", ability to metabolize different carbon sources and enzymatic activity (only bacteria from mulungu), their “in vitro” plant growth promotion mechanisms by means of the production of indole acetic aci d (IAA) and calcium phosphate solubilization and finally tested in the greenhouse with the original 2 host plants, to determine the symbiotic efficiency of the isolates. Isolates of mulungu showed variability for enzyme activity and metabolism of carbon sources. Five isolated mulungu and jurema-preta and 6 isolates from angico were able to produce IAA in L-tryptophan supplemented medium, reaching rates above those achieved by the reference strain. As the potential of calcium phosphate solubilization for mulungu isolates, only one bacteria was able to achieve high solubilization equal to the reference strain, seven and two isolates from jurema-preta and angico, solubilized calcium phosphate above the reference strains value. For each species there bacteria were able to show tolerance to high temperatures and salinity. Isolates of angico and jurema were submitted to ARDRA using three endonucleases: MspI, HinfI and HhaI. The genetic diversity evaluation indicated that to angico a large cluster with around 40% of similarity was formed. To jurema-preta a major cluster with 65% of similarity among the isolates were achieved. In addition to high diversity of bacteria, patterns regarding its geographical occurrence were also observed. Bacteria from mulungu had the sequences of the 16S rRNA gene partially determinated. Among the 13 bacteria with good sequences, six belong to Rhizobium, six Bradyrhizobium and one belongs to Burkholderia. The Efficiency of tests, 22 isolates of mimosa and 10 mulungu were able to renodulate their original host strains and A27 from Angico and M14 and M31 can be highlighted to mulungu.