Abstract
A significant number of bacterial species, particularly in the rhizosphere, may benefit plant growth and development. This group of bacteria is known as plant growth-promoting rhizobacteria (PGPR). This study identified genetically isolates of common bean nodules used to trap bacteria from Amazon pastureland and investigated their capacity of nodulating and promoting growth of common bean when inoculated or co-inoculated with CIAT899 strain (Rhizobium tropici). Two experiments were carried out in a greenhouse, in axenic conditions, using the common bean cultivar Talismã. In the first experiment, 56 PGPR strains were evaluated individually regarding growth promotion and nodulation. In the second experiment, inoculation of seven PGPR strains previously selected in the first experiment was evaluated in three forms of N supply: Co-inoculation with CIAT 899 in the presence of low N-mineral concentration; individual inoculation in the presence of high N-mineral concentration; and individual inoculation in the presence of low N-mineral concentration. The 16S rRNA gene sequencing showed predominance of Pseudomonas genus, identified in 35 % of the sequenced strains. Other genera were identified: Rhizobium, Burkholderia, Xanthomonas and Bacillus. Inoculation of the seven strains with CIAT 899 promoted distinct plant growth in different forms of N supply. In addition, N-mineral supply can be replaced by co-inoculation with strains of Pseudomonas sp. (UFLA 02-281 and UFLA 02-293) and Bacillus sp. (UFLA 02-298) identified in this study.
Highlights
In the search for promising isolates that promote plant growth, the Amazon region stands out for its high diversity of organisms in the soil, including microorganisms
This study identified genetically isolates of common bean nodules used to trap bacteria from Amazon pastureland and investigated their capacity of nodulating and promoting growth of common bean when inoculated or co-inoculated with CIAT899 strain (Rhizobium tropici)
A comparison of the 16S rRNA gene partial sequencing of strains evaluated with sequences deposited in the GenBank revealed that strains belong to Rhizobium, Burkholderia, Xanthomonas, Brevibacillus, and Bacillus genera, with predominance of Pseudomonas (Table 2)
Summary
In the search for promising isolates that promote plant growth, the Amazon region stands out for its high diversity of organisms in the soil, including microorganisms. Co-inoculation of Rhizobium and plant growth-promoting rhizobacteria (PGPR) in legumes have received more attention in recent years (Tilak et al, 2006; Mishra et al, 2011; Samavat et al, 2012). This combination brings positive effects on the cultivation of legume species, since it provides growth and nutrient absorption, as it happens in lentil plants with the co-inoculation of Pseudomonas sp. This combination presents positive effects on grain yield, as it happens in bean crop, with the co-inoculation of Pseudomonas and Rhizobium (Samavat et al, 2012)
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