Isolation and characterization of soybean‐associated bacteria and their potential for plant growth promotion

TLDR

Bacteria were isolated from two soybean cultivars and identified by partial 16S rDNA sequencing, revealing members of Pseudomonaceae, Burkholderiaceae, and Enterobacteriaceae. Population densities varied with season, growth stage, and tissue, and 34 % of endophytic and 21 % of epiphytic isolates produced indole‑acetic acid while 49 % and 52 % solubilized phosphate, respectively; high IAA producers were found in early‑ripening Foscarin and high phosphate solubilizers in V6 plants, with 60 % of endophytic and 69 % of epiphytic IAA/ phosphate producers also fixing nitrogen, and the plant‑growth‑promoting strains belonged to Pseudomonas, Ralstonia, Enterobacter, Pantoea, and Acinetobacter.

Abstract

Endophytic and epiphytic bacteria were isolated from two soybean cultivars (Foscarin and Cristalina). Significant differences were observed in bacterial population densities in relation to season of isolation, soybean growth phase and the tissues from which the isolates were obtained. The isolates were identified by partial 16S rDNA sequence analysis, with most of the isolates belonging to the Pseudomonaceae, Burkholderiacea and Enterobacteriaceae groups. The potential of the isolates for plant growth promotion was evaluated by screening for indoleacetic acid (IAA) production and mineral phosphate solubilization; 34% of endophytic bacteria produced IAA and 49% were able to solubilize mineral phosphate whereas only 21% of epiphytic bacteria produced IAA although 52% were able to solubilize mineral phosphate. A high frequency of IAA producing isolates occurred in the early ripening Foscarin cultivar whereas a high percentage of phosphate solubilizing isolates were obtained from plants in the initial development stage (V6). We also found that 60% of endophytic and 69% of epiphytic isolates that produced IAA and solubilized mineral phosphate were also able to fix nitrogen in vitro. The soybean-associated bacteria showing characteristics related to plant growth promotion were identified as belonging to the genera Pseudomonas, Ralstonia, Enterobacter, Pantoea and Acinetobacter.