Diversidade genética e simbiótica de bactérias fixadoras de nitrogênio isoladas de solos sob agrofloresta na Amazônia Ocidental usando o caupi como planta isca

Abstract

The objective of this study was to evaluate the genetic diversity and symbiotic efficiency nitrogen-fixing bacteria isolated from nodules of the trap plant cowpea inoculated with soils under agroforestry in the Western Amazon. The isolates were obtained in previous work, from a collection of 1010 isolates from different land used systems which included 188 from agroforestry. Initially, we confirmed cultural characteristics previously described by using 79 medium. Of the 188 isolates, 148 were still viable. Experiments for authentication and symbiotic efficiency of these isolates were performed in greenhouse, in a completely randomized design with three replications. We used amber glass recycled bottles (500 mL), containing Hoagland solution diluted four times, and the cowpea (BR17 Gurguéia) as host plant. Control treatments were without inoculation (with and without mineral nitrogen) and inoculated with strains recommended as inoculants INPA 03-11B, UFLA 03-84, BR 3267. The authentication was evaluated through nodules presence (+) or absence (-) in inoculated plants. The symbiotic efficiency was evaluated 35 days after emergence, when it was determined the SPAD (Soil Plant Analysis Development) which is an indirect measurement of the nitrogen content, number and dry weight of nodules, dry and fresh matter shoot weight and relative efficiency. The data were subjected to analysis of variance and group of averages by means of the Scott-Knott test in a probability of 5%. 88 isolates showed positive nodulation and were subjected to analysis of polymorphism in DNA, with the aim of evaluating their diversity by using the BOX-PCR technique. This analysis included the type strains Azorhizobium dobereinerae (BR5401T), Azorhizobium caulinodans (ORS571T), Cupriavidus taiwanensis (LMG19424T), Burkholderia sabiae (BR3405), Mesorhizobium plurifarium (BR3804), Bradyrhizobium sp. (UFLA 03-84) and Sinorhizobium sp. (BR6806). Partial sequences of the 16S rDNA of 20 isolates were obtained and phylogenetically analyzed. According to the cultural, nine groups were formed. The symbiotic isolates was variable and 12.5% of isolates promoted a statistically significant increase in dry matter of shoots, compared to the control without inoculation and without mineral nitrogen. It was founding high genetic diversity: at the level of 70% similarity, 72 groups were found, most consisting of only one isolate. The predominant genus was Bradyrhizobium, identified for 55% of the isolates sequences. The more efficient isolate in nitrogen fixation was identified as Rhizobium sp. We also identified other generous, such as Paenibacillus, Stenotrophomonas, Enterobacter, Ochrobactrum and Bosea. These results showed high genetic diversity and symbiotic efficiency in soils under the these land-use agroforestry in the Western Amazon.