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.
