Isolation of Burkholderia cepacia JBK9 with plant growth-promoting activity while producing pyrrolnitrin antagonistic to plant fungal diseases

Burkholderia species are widely distributed across wide ecological niches. Many genera of Burkholderia are known to be associated with plants and are involved in processes such as suppression of soil-borne pathogens, acceleration of plant growth and endophytic colonization. In the present study, a strain belonging to the Burkholderia cepacia complex, which was termed JBK9, was isolated. The strain JBK9 showed broad-spectrum antifungal activities against Phytophthora capsici, Fusarium oxysporum, and Rhizoctonia solani, which are representative phytopathogenic fungi, inhibiting their growth by 59.56, 51.92, and 34.22%, respectively. The strain produced an antifungal compound that was confirmed to be pyrrolnitrin by TLC, HPLC, and NMR analyses. Using an in vitro assay for plant root colonization, we observed that the population densities of B. cepacia JBK9 on the upper 1 cm of host plant roots were significantly different between Burkholderia species. The high motility of these strains is likely to have contributed to their efficient root colonization. The isolated strain was evaluated in vivo for its ability to control Phytophthora blight via a pot test. Compared with Burkholderia strains KCTC 2973 and ATCC 25416, B. cepacia JBK9 demonstrated a stronger antifungal activity against P. capsici. The strain B. cepacia JBK9 could be further developed as a biological control agent for pepper plants.