A total of 40 endophytic bacterial isolates obtained from banana tree roots were characterized for their biotechnological potential for promoting banana tree growth. All isolates had at least one positive feature. Twenty isolates were likely diazotrophs and formed pellicles in nitrogen-free culture medium, and 67% of these isolates belonged to the genus Bacillus sp. The isolates EB-04, EB-169, EB-64, and EB-144 had N fixation abilities as measured by the Kjeldahl method and by an acetylene reduction activity assay. Among the 40 isolates, 37.5% were capable of solubilizing inorganic phosphate and the isolates EB-47 and EB-64 showed the highest solubilization capacity. The isolate EB-53 (Lysinibacillus sp.) had a high solubilization index, whereas 73% of the isolates had low solubilization indices. The synthesis of indole-3-acetic acid (IAA) in the presence of L-tryptophan was detected in 40% of the isolates. The isolate EB-40 (Bacillus sp.) produced the highest amount of IAA (47.88 μg/ml) in medium supplemented with L-tryptophan and was able to synthesize IAA in the absence of L-tryptophan. The isolates EB-126 (Bacillus subtilis) and EB-47 (Bacillus sp.) were able to simultaneously fix nitrogen, solubilize phosphate and produce IAA in vitro. The results of this study demonstrated that the isolates analyzed here had diverse abilities and all have the potential to be used as growth-promoting microbial inoculants for banana trees.

The objective of this study was to characterize banana tree endophytic bacteria at genus and species level and to determine the metabolic reactions associated with the nitrogen transformations. The identification at genus and species levels was performed using the partial sequencing of the rDNA 16S region. The assimbyotic nitrogen fixation, the reduction of nitrate and the production of urease were in vitro evaluated. The DNA of the bacterial isolates was also amplified to verify the presence of the nifH, nirK and nirS regions. Biochemical tests were performed in a complete randomized design; the treatments consisted of 39 bacterial isolates with three replications. Sequence analysis enabled the identification of four genera: Bacillus, Rhizobium, Klebsiella and Enterobacter. The Bacillus genus occurred more frequently, nine species were identified. By evaluating the results of biochemical tests, it was observed that three isolates showed multiple abilities: growth in NFb medium, nitrate reduction and production of urease. The isolates belong to the genus Bacillus and of the species subtilis, thuringienses and amyloliquefaciens. Approximately 12.5% of the isolates amplified the region corresponding to the nifH gene, 7.5% amplified gene nirK and 3.9% amplified the nirS gene. Endophytic bacteria evaluated in the present study showed in vitro activity for urease, nitrate reductase enzymes, however, relevant nitrogenase activity was not observed.

Phomopsis sojae and Sclerotinia sclerotiorum are responsible for stem and pod dryness and white mold in soybean. These pathologies directly affect the quality of seeds/grains and compromise the entire plant. The use of extracts from different plants has been the subject of research for the control of several phytopathogens. Calotropis procera is among botanical species that synthesize efficient compounds for biocontrol. In this context, the aim of this study was to evaluate the in vitro effect of C. procera aqueous extract on P. sojae and S. sclerotiorum. The experiment was carried out in completely randomized blocks in a 2 × 5 factorial scheme (two fungi and five extract concentrations 0%, 5%, 10%, 15% and 20%) with 4 replicates. C. procera aqueous extract concentrations were added to Petri dishes containing PDA. After 48 hours, the mycelial growth rate was evaluated. After seven days of incubation, the fungal colony area, sporulation, and germination of P. sojae and S. sclerotiorum were evaluated. There was significant interaction between fungi × extract concentrations (p < 0.05) for all variables analyzed. The mycelial growth rate of P. sojae was lower than that of S. sclerotiorum. The diameter of the P. sojae fungal colony was smaller than that of S. sclerotiorum when concentrations of 5%, 10% and 15% were used. As the extract concentration increased, fungi sporulation and germination reduced.