Characterization of plant growth-promoting traits and antagonistic potentials of endophytic bacteria from bean plants against Pseudomonas syringae pv. phaseolicola

Abstract

Pseudomonas syringae pv. phaseolicola (Psp) is a seed-borne bacterium which causes halo blight disease in common bean. This study aimed the determination of plant growth-promoting traits (such as IAA, phosphate solubilization) and antagonistic potentials (such as siderophore and ammonia productions) of endophytic plant growth-promoting bacteria (PGPB) from healthy bean plants growing in different regions against Psp in vitro conditions. A total of 131 bacteria were primarily characterized as putative PGPB and tested for antagonist activity against Psp in dual culture tests. Seventy-one bacterial isolates demonstrated antagonistic activities against Psp isolate in varying ratios. Among these 71 isolates, 30 representative bacterial isolates from the different regions/fields were selected. On the basis of morphological, physiological, biochemical characteristics and confirmation by MALDI-TOF analyses, 30 endophytic antagonist isolates were identified as belonging to 10 genera, 24 different species. According to results obtained, 10 isolates belong to Bacillus spp., 6 isolates belong to Pseudomonas spp., 4 isolates belong to Rhizobium radiobacter, 2 isolates belong to Arthrobacter spp., 2 isolates belong to Achromobacter spanius, 2 isolates belong to Serratia liquefaciens, 1 isolate belongs to Acinetobacter calcoaceticus, Exiguobacterium sp., Microbacterium hydrocarbonoxydans, and Ochrobactrum anthropi. The largest and lowest inhibition zone was produced by endophytic bacterial isolates Pseudomonas gessardii (4.85) and Bacillus licheniformis (1.35). Among the tested antagonist bacterial isolates, 10 isolates were positive for the production of α-amylase, 7 isolates positive for phosphate solubilization, 29 isolates positive for siderophore production, 11 isolates positive for protease production. All selected bacterial isolates produced IAA and ammonia in relatively varying amounts. P. gessardii produced a relatively large amount of extracellular siderophore (5.83), Exiguobacterium sp. produced a relatively large amount of extracellular protease (5.25), P. gessardii and O. anthropi produced a relatively large amount of extracellular IAA (161.39 µg/ml) and Acinetobacter calcoaceticus produced a relatively large amount of phosphatase (2.63). This is the first study reporting bean plants harbor endophytes having plant growth promoting activities with antagonistic potential against Psp.