Symptom development of pine wilt disease. Histopathological observations with electron microscopes.

Abstract

One year-old seedlings of Pinus densiflora were inoculated with pine wood nematode, Bursaphelenchus xylophilus. Tissue samples were examined under SEM and TEM. In in- oculated stems, living cells of cambia, resin canals and rays began to degrade within a few days of inoculation. Severe and early degradation of the cambial zone had appeared, partic- ularly in samples taken from the stem base. Dissolution patterns appeared in cell walls suggesting strong cellulose decomposing activity of the nematode. Systematic death of living cells in the stem base was thought to be responsible for the death of the whole seedling.