The specialization ofEsteya vermicolahyphae in infection toBursaphelenchus xylophilusand its colonization of pine tree
Authors: Wang Hai-Hua , Yin Can , Gao Jie , Tao Ran , Dai Piao-Piao , Wang Chun-Yan , Sung Chang-Keun 
Published: August 2020

Pine wilt disease (PWD) caused by the nematodeBursaphelenchus xylophilusis a serious problem on pines, and there is currently no effective control strategy for this disease. Although the endoparasitic fungusEsteya vermicolashowed great effectiveness in controlling pine wilt disease, the colonization patterns of the host pine tree xylem by this fungus are unknown. To investigate the colonization patterns of pine xylem by this fungus, the speciesPinus koraiensisgrown in a greenhouse was used as an experimental host tree. The fungal colonization of healthy and wilting pine trees byE. vermicolawas quantified using PCR with a TaqMan probe, and a green fluorescence protein (GFP) transformant was used for visualization. The results reported a specific infection approach used byE. vermicolato infectB. xylophilusand specialized fungal parasitic cells in PWN infection. In addition, the inoculated blastospores ofE. vermicolagerminated and grew inside of healthy pine xylem, although the growth rate was slow. Moreover,E. vermicolaextended into the pine xylem following spray inoculation of wounded pine seedling stems, and a significant increase in fungal quantity was observed in response toB. xylophilusinvasion. An accelerated extension ofE. vermicolacolonization was shown in PWN-infected wilting pine trees, due to the immigration of fungal-infected PWNs. Our results provide helpful knowledge about the extension rate of this fungus in healthy and wilting PWN-susceptible pine trees in the biological control of PWD and will contribute to the development of a management method for PWD control in the field.

Author summary

Pine wilt disease, caused byBursaphelenchus xylophilus, has infected most pine forests in Asian and European forests and led to enormous losses of forest ecosystem and economy.Esteya vermicolais a bio-control fungus against pinewood nematode, showed excellent control efficient to pine wilt disease in both of greenhouse experiments and field tests. Although this bio-control agent was well known for the management of pine wilt disease, the infection mechanism of fungal infection and colonization of host pine tree are less understand. Here, we use GFP-tagged mutant to investigate the fungal infection to pinewood nematode; additionally, the temporal and spatial dynamics ofE. vermicolacolonize to pine tree were determined by the TaqMan real-time PCR quantification, as well as the response to pinewood nematode invasion. We found a specific infection approach used byE. vermicolato infectB. xylophilusand specialized fungal parasitic cells in PWN infection. In addition, the fungal germination and extension inside of pine tree xylem after inoculation were revealed. In addition, the quantity ofE. vermicolaincreased as response to pinewood nematode invasion was reported. Our study provides two novel technologies for the visualization and detection ofE. vermicolafor the future investigations of fungal colonization and its parasitism against pinewood nematode, and the mechanisms of the bio-control process.