The Relationship Between the Pinewood Nematode (PWN) and Fungi Cohabiting in aine Trees Inoculated with the PWN

Abstract

The relationship between the pinewood nematode (PWN) and fungi cohabiting with the nematodes in 15-year-old Japanese black pine (Pinus thunbergii) was examined bimonthly over a year after inoculation with PWN. The population of PWN in the trees was high in August, but slightly decrease in December then increased again in February. From wood samples of the pine trees examined, 18 species of fungi have been isolated. Among the 18 fungi detected, Phialophora repens, Sphaeropsis sapinea, Pestalotiopsis sp., Rhizoctonia sp. were the most frequently isolated in every season. All of these fungi had positive effects on the increase of nematode population, though the population of PWN on Rhizoctonia sp. was less than those on the other three dominant fungi. Under laboratory conditions, 19 species of fungi cultured on potato dextrose agar (PDA) served for PWN as food source, and the PWN’s population built up on each fungus was compared at 20 ˆC. PWN dramatically increased on Pestalotiopsis sp. 1, Pestalotiopsis sp. 2, Sphaeropsis sapinea, Phialophora repens, and Botrytis cinerea (control), from 10 to 15 days after inoculation. From the point of view in terms of the food quality and their cohabitating ability we conclude that the species of fungi that are dominant in pine trees, except Rhizoctonia sp., have a compatible relationship with the PWN, while Rhizoctonia sp. and Penicillium sp. proved to be neutral, and Trichoderma sp. an incompatible relationship with PWN.