DIFFERENT INCIDENCES OF PINE WILT DISEASE IN PINUS-DENSIFLORA SEEDLINGS GROWING WITH DIFFERENT TREE SPECIES

Field-grown Japanese red pine (Pinus densiflora) seedlings were inocul ated with the pine wood nematode (Bursaphelenchus xylophilus) in early July 1991 to clarify the effect of co-occurring tree species on the s usceptibility of P. densiflora to pine wilt disease. Sixteen weeks aft er inoculation, 48, 33, 14, and 18% of pine seedlings were diseased wh en they grew with Abnus sieboldiana, with Sarothamus scoparius, with t he naturally associated species of P. densiflora such as Ilex peduncul osa and Eurya japonica, and in a pure stand of P. densiflora, respecti vely. When associated with A. sieboldiana or S. scoparius, pine seedli ngs quickly had visual discoloration of foliage. Twenty percent of P. densiflora seedlings treated with water died within 6 months when grow ing in the stand with A. sieboldiana, suggesting that the seedlings we re stressed. The susceptibility of P. densiflora seedlings to pine wil t disease was enhanced by the different tree species co-occurring with the seedlings.