Simbiose entre Crotalaria spp. e bactérias de nódulos naturalmente estabelecidas em solos da Zona da Mata de Pernambuco

Abstract

Brazil is experiencing the greatest success in the use of biological nitrogen fixation (FBN) in agricultural systems and, recently, has been positioning itself on the international scene with the description of new species of rhizobia. The diversity of combinations of types and soil cover makes the Zona da Mata of Pernambuco a region with great potential for studies of rhizobia ecology and for the search for new elite strains for biological nitrogen fixation (FBN). This project aims to estimate the occurrence and diversity of nodule bacteria from different species of the Crotalaria genus to make a collection available for obtaining inoculants for recommendation for green manure in soils in the Zona da Mata of Pernambuco. Initially, a representative sampling of the different edaphoclimatic conditions of the Zona-da-Mata de Pernambuco was carried out, encompassing soils of the main types and uses of soil in the region, at points defined according to the class requirements and soil cover. The soil classes were selected at the 1st categorical level, namely: ARGISSOLO, LATOSSOLO and GLEISSOLO, which together represent about 85% of the region's soils. Four types of vegetation cover, which are predominant in the Zona-da-Mata de Pernambuco, were defined: 1) cultivation with sugarcane; 2) capoeira; 3) other agricultural uses and 4) native vegetation (forest). The natural occurrence of populations of bacteria capable of forming nodules with three species of Crotalaria spp., As well as the development of plants grown in the collected soil samples were determined in experiments carried out in pots in a greenhouse. This experiment was also used as a bait plant test to isolate nodule bacteria from plants grown in soil samples representative of each situation. A collection of 505 nodule bacteria was obtained, which was characterized phenotypically in YMA culture medium. In isolates representative of the phenotypic groups used, an initial genetic profile of the populations naturally established in the studied soils was traced, through the evaluation of the genetic variability of the isolates using the techniques of BOX-PCR and Restriction Analysis of Amplified Ribosomal DNA (ARDRA). The joint analysis of the restriction profiles of the 16S rRNA, obtained from the endonucleases: Alu I, Xba I, Apa I, Xho I, Rsa I, Hae III and Nde I allowed the formation of groups of isolates with similarity, and according to with the distribution of the strains, it consisted of the separation of the isolates in the soil classes. This grouping points to genetic variability of the isolates and indicates a possible existence of taxonomic, among the isolates obtained, not yet known in the literature.