A study on endophytic bacteria isolated from wild legumes against Xanthomonas phaseoli

Common bacterial blight disease (CBB) of bean (Phaseolus vulgaris) caused by Xanthomonas phaseoli (Xp) is considered as one of the most deleterious pathogens for bean production in the world. In this study, 105 samples were collected from asymptomatic wild fabaceous plants, i.e. Astragalus ovinus, Vicia villosa and Vicia lutea, grown in Zagros forests of Iran. The plant samples were cultured on nutrient agar and purified. The isolates were then screened for some important criteria for biological control such as phosphate solubilization, protease activity, IAA and H2S production, and antagonistic effect. Three endophytic bacterial isolates were found as potential biocontrol agents against Xp. Based on key biochemical tests and comparative analysis of the partial 16S rDNA sequences, the isolates were identified as Pseudomonas fluorescens and two Bacillus species. Under greenhouse conditions, all the three strains significantly increased shoot and root lengths in bean plants at the 5% level (P < 0.05) and decreased disease severity above 70%. This is the first report on the presence and capabilities of endophytic bacteria from wild leguminous plants in the Zagros Mountain steppe forests of Iran.