Unraveling the interactions of Esteya vermicola, pinewood nematode, and pine hosts: Insights into population dynamics and molecular responses.

Esteya vermicola has shown promise as an efficient biological control agent against pine wilt disease, a devastating disease in pine forests caused by the pinewood nematode (PWN, Bursaphelenchus xylophilus). However, the in vivo interactions among E. vermicola, PWN, and pine hosts are less understood, both at the population and molecular levels. In this study, we performed a series of bioassays to investigate E. vermicola colonization patterns in pine xylem and its population responses to PWN invasion in healthy and PWN-induced wilting trees. Our results demonstrated that although E. vermicola exhibits slow growth, its conidia germinate and grew along the pine tracheid, even producing lunate conidia capable of initiating PWN infections within the xylem. Interestingly, while fungal hyphae became undetectable in pine sapling xylem after inoculation, the E. vermicola population increased immediately in response to PWN invasion. Furthermore, we observed a "leap-frog" dispersal pattern of fungal colonization in PWN-induced wilting pines, facilitated by the migration of fungal-infected nematodes. Moreover, we explored the molecular mechanisms underlying fungal tolerance to pine defense systems using transcriptomic analysis. Comparative transcriptomics revealed that carbohydrate metabolism and abiotic stress-induced oxidoreductive activities are involved in the fungal tolerance to the pine defense compound ß-pinene. This study enhances our understanding of how E. vermicola colonizes and persists within pine xylem, its molecular responses to plant defense compounds, and its population dynamics upon PWN invasion, validating its efficacy as a biocontrol agent against pine wilt disease.

Esteya vermicola Controls the Pinewood Nematode, Bursaphelenchus xylophilus, in Pine Seedlings.

Esteya vermicola (Ophiostomataceae) is an endoparasitic fungus that has great potential as a biological control agent against the pinewood nematode Bursaphelenchus xylophilus which causes pine wilt disease. We tested E. vermicola for control of pine wilt disease by spraying E. vermicola conidia on artificial wounds on pine seedlings, and the optimum E. vermicola treatment density and application time were also investigated in the greenhouse. The wounds were similar to those made by sawyer beetles (Coleoptera: Cerambycidae). Esteya vermicola treatments significantly increased the survival rate of pine seedlings that were infected by pinewood nematodes. Wounded plants sprayed with 107 CFU/ml E. vermicola had a 73.0% greater survival rate than nonwounded pine seedlings treated similarly. The treatment of pine seedlings with 107 CFU/ml E. vermicola 14 d before nematode infection increased their survival rate by 90.0%. The number of pinewood nematodes isolated from dead pine seedlings sprayed with E. vermicola was 76% less than the number of pinewood nematodes in the controls. Moreover, infected nematodes and the hyphae of E. vermicola were detected in the dead or wilting pine seedlings. Therefore, spraying E. vermicola on the wounds of pine seedlings made by sawyer beetles provides good control of the pine wilt disease that is caused by pinewood nematodes.