Hypothesized mechanism of biocontrol against pine wilt disease by the nematophagous fungus Esteya vermicola

Esteya vermicola is an endophytic fungus of pine wood nematode(s) (PWN) Bursaphelenchus xylophilus and a promising biocontrol agent. However, until now, only the lunate spores of E. vermicola have been demonstrated to be highly effective against pine wilt disease. In the present study, blastospores of E. vermicola were successfully used as a biocontrol agent through injection into large pine trees in Aewol-eup, Jeju, South Korea. When pine trees were injected with a 6–8 mL blastospore suspension of E. vermicola (108 mL−1) 1 month before inoculating them with PWN, 73.77% of the trees remained alive after one year. When injected with blastospores of E. vermicola 2 and 4 weeks after PWN infection, 40% of the trees were saved. As a control, the pine trees inoculated with PWN only all died. Moreover, a hypothesis of the mechanism of biocontrol within the pine tree was proposed based on the population density of PWN over time along with the presence of E. vermicola in the pine tree. The hypothesis involved a cycle that included the growth of E. vermicola without PWN infection, attraction and adhesion to PWN, movement and death of infected PWN, production of a second generation of lunate spores, and attraction of other migratory PWN.