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Sahashi N.,Laboratory of Forest Pathology | Akiba M.,Laboratory of Forest Pathology | Ishihara M.,Japan Forestry and Forest Products Research Institute | Miyazaki K.,Japan Forestry and Forest Products Research Institute | Kanzaki N.,Laboratory of Forest Pathology
Plant Disease | Year: 2010

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 Bischofia javanica 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. © 2010 The American Phytopathological Society.

Sahashi N.,Japan Forestry and Forest Products Research Institute | Sahashi N.,Laboratory of Forest Pathology | Akiba M.,Japan Forestry and Forest Products Research Institute | Akiba M.,Laboratory of Forest Pathology | And 4 more authors.
Mycological Progress | Year: 2010

Cylindrobasidium argenteum, a causal pathogen of white stem blight of a variety of broadleaf trees and shrubs, is thought to be transmitted to healthy trees through contact with infected branches of neighboring trees. To clarify whether basidiospores of C. argenteum are involved in the dispersal and infection process, we investigated distribution of genets of the fungus in a river valley forest using a somatic incompatibility test. Thirty-eight isolates were collected from diseased trees along two census lines at the bottom of Kikuchi River valley in southern Japan. In addition, 50 isolates were collected from four experimental plots on the slope of the valley. When the isolates from the valley bottom were paired in all combinations, a narrow clear zone line appeared in 701 out of 703 pairings, indicating that the material included 36 different genotypes, and suggesting that airborne basidiospores play an important role for dispersal of C. argenteum. In contrast, vegetative spread proved to be more frequent on the slope of the valley. On lower parts of such slopes, opportunities for healthy trees to meet infectious agents may increase because infected broken branches frequently move downwards on the slope. Based on these results, we suggest that C. argenteum adopts following dissemination strategies: (1) it spreads chiefly by basidiospores and infects trees, and (2) after colonizing stems or branches and producing an extensive mycelial mat, secondary infections of adjacent trees occur by contact with infectious agents such as diseased branches. © 2010 German Mycological Society and Springer.

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