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Pine wilt disease is one of the most serious epidemic tree diseases in Japan, and resistant pine trees have been developed through a breeding program. To evaluate resistance of resistant families of Japanese black pine, Pin us thunbergii, to the pinewood nematode, Bursaphelenchus xylophilus, isolated from the field, and to determine whether differentiation of pathogenicity to resistant pine families appears in the nematode isolates, seedlings of five resistant pine families were inoculated with 25 nematode isolates. Disease incidence 18 weeks after inoculation was significantly different among nematode isolates and among pine families but there was no interaction effect between nematode isolate and pine family. This indicates that nematode isolates did not have differential host specificity to resistant families of P. thunbergii. Isolate Shimabara, a test isolate of the breeding program, showed the same degree of virulence as the highly virulent isolates frequently used in experiments. However, more virulent isolates than Shimabara were found among the isolates collected from natural pine forest. This indicated that B. xylophilus populations with higher virulence than Shimabara exist in the natural population. These findings are important in development of more efficient breeding procedures for resistant pine trees. [ABSTRACT FROM AUTHOR]

Brown root rot, caused by Phellinus noxius, leads to problems in management of shade, ornamental, and windbreak trees in subtropical regions of the world, and it has been causing serious problems in Japan since 1988. To identify the pathogenicity, host specialization, and virulence of the pathogen, cross inoculation tests were carried out using isolates of the fungus obtained from nine different tree species. P noxius was pathogenic to all of the nine tree species tested, and it killed inoculated seedlings. Among the 810 trees inoculated with the fungus, a total of 141 trees (17.4%), including all nine species, were dead within 110 days after inoculation. The first symptom of infection was rapid wilt with discoloration of leaves 20 to 30 days after inoculation, and then the plants quickly declined. Only one isolate of P. noxius that was tested caused significantly higher mortality in its original host than in other species, suggesting that the pathogen has little to no host specificity. However, the fungus did show variation in virulence, with the isolates originating in Bischofiajavanica and Casuarina equisetifolia causing significantly higher mortality than those collected from other host species. More isolates of P noxius from the same host species and/or from various countries should be studied to understand host specialization and virulence of the pathogen. [ABSTRACT FROM AUTHOR]