Forestry and Forest Products Research Institute, Tsukuba, Japan

Background and objectives
Armillaria root rot occurs on plantations of conifers including Hinoki cypress [Chamaecyparis obtusa (Sieb. et Zucc.) Endlicher], an important species for wood production in Japan. A. mellea and A. ostoyae are frequently isolated from diseased conifers[1]. Although Japanese A. mellea was reported to show pathogenicity when inoculated on conifers, reports on inoculation test of Japanese A. ostoyae is rather few. The objectives of this test are to examine pathogenicity of Japanese A. ostoyae by inoculation test, and to compare it with that of North American A. ostoyae, which was reported to be pathogenic on conifers [2]. Isolates of Japanese A. mellea and A. gallica were also used in comparison.

Materials and methods
One isolate of Japanese A. ostoyae from a severely damaged plantation, two Canadian A. ostoyae, one Japanese A. mellea> and two A. gallica were used in this study. Branch segments(8 x 1cm) of an oak(Quercus serrata Murray) were autoclaved, inoculated with the isolates and used as inocula after incubation. Cuttings of Hinoki cypress of the same clone were planted in clay pots with the soil and test tubes 2 year after cutting. The next year, test tubes were excised and replaced by inocula. 10 cuttings were prepared to inoculate each isolate. Hinoki cypress were placed outside and supplied water once a day. 4 years after inoculation, roots of the Hinoki cypress were examined for infection.

Results and conclusions
Japanese A. mellea infected on 5 Hinoki cypress and killed 3, and one Canadian A. ostoyae infected on 2 and killed 1. Other isolates caused no infection nor mortality. After the inoculation test, most of the inocula of all the isolates except Japanese A. ostoyae had thick mycerial mats under the bark which is typical for Armillaria colonization. None of the inocula of Japanese A. ostoyae had mycerial mat. Japanese A. mellea and North American A. ostoyae have pathogenicity on Hinoki Cypress. The fact that only one Canadian isolate of the two showed pathogenicity consists with previous reports that pathogenicity of A. ostoyae ranges from mild to aggressive depending on isolates[2]. Japanese A. ostoyae showed no pathogenicity in this test. One reason for this would be death of the fungus in inocula in early stage of the experiment. Therefore it may cause infection and mortality if inocula were kept in good condition for long time. Inocula of A. gallica kept good condition until the end of this test but caused no infection, showing no pathogenicity of this species on Hinoki cypress.

1. Hasegawa, E, 1994. 5th International Mycological Congress Abstract, p.85.
2. Shaw, C G III, Kile, G A, 1991. Armillaria Root Disease. 233pp, Agriculture Handbook No. 691, USDA Forest Service, Washington, D. C.