Broad spectrum anti-biotic activity and disease suppression by the potential biocontrol agent Burkholderia ambifaria BC-F

Abstract

The potential biocontrol bacterium Burkholderia ambifaria isolate BC-F significantly suppressed damping-off of cucumber and soybean caused by Pythium ultimum when applied as a seed coating. Cucumber and soybean seed coated with a peat bond formulation of isolate BC-F had significantly greater plant stands than the non-treated pathogen controls in soil-less mix. Soybean seeds treated with isolate BC-F had significantly greater plant fresh weight per pot and plant height per pot than the pathogen control. Isolate BC-F effectively colonized the roots of corn, cucumber, soybean, and sunflower and was detected at ⩾10 5 colony-forming-units per gram fresh weight of root after 4 weeks in two different natural soils. Burkholderia ambifaria BC-F grown on nutrient broth agar or potato dextrose agar released a diffusable metabolite(s) that inhibited hyphal growth of P. ultimum, Rhizoctonia solani, Phytophthora capsici, and Fusarium oxysporum f.sp. lycopersici. Culture filtrates from isolate BC-F grown on nutrient broth contained a metabolite(s) that inhibited egg hatch and mobility of second-stage juveniles of Meloidogyne incognita. These culture filtrates contained chitinase and protease activities. However, the <3 kDa fraction of these culture filtrates was responsible for the inhibition of M. incognita. The >8 kDa fraction contained no inhibitory activity, indicating that inhibition of egg hatch and mobility of second-stage juveniles of M. incognita was not directly due to chitinase and protease activities. The demonstrated ability of isolate BC-F to suppress disease caused by animal and fungal pathogens of many crop plants may be due to the ability of isolate BC-F to persist for long periods in association with roots of diverse crop plants in different soils and the production of a metabolite(s) with broad spectrum anti-biotic activity.