Bacterial endophytes isolated from mountain-cultivated ginseng (Panax ginseng Mayer) have biocontrol potential against ginseng pathogens

Ginseng (Panax ginseng Meyer) is a perennial medicinal plant. Long cultivation practice makes ginseng vulnerable to attack by various biotic constrains. The biocontrol of ginseng pathogens with microbes is an important alternative to chemical control. We screened 252 bacterial endophytes isolated from mountain-cultivated ginseng against 6 ginseng pathogens. Twelve bacterial endophytes were selected using a dual culture assay. Overall, Burkholderia stabilis EB159 (PG159) exerted the greatest inhibitory activity against all ginseng pathogens (42.3-84.7% inhibition). Cell-free supernatant and ethyl acetate extracts of PG159 exerted significant antagonistic effects against all pathogens (37.3-100 and 30.6-100%, respectively). Direct treatment of Botrytis cinerea with PG159 cell-free supernatant down-regulated pathogen genes involved in growth and virulence (BCG1, BOT1, PKA1 and TRE1). Direct inoculation of ginseng roots with PG159 by dipping induced genes involved in defense, either in above- or below-ground parts of ginseng plants (PR2, PR3, PR4, PR5, PR6 and PR10). B. cinerea genes involved in growth (BCG1, BAC, PKA1, CHS3 and TRE1) were also down-regulated in PG159 pre-inoculated plants. PG159 inoculation significantly reduced the disease area induced by B. cinerea in ginseng leaves.