Armillaria species are widely distributed from the boreal to subtropical areas. Some of them are well known as pathogens that cause root rot disease on many conifers and hardwoods. Recent studies using molecular techniques gain the information about taxonomy, phylogeny and genetic relationship. In this paper, taxonomy, phylogeny, ecology and control of Armillaria spp. were briefly reviewed. The topic of the relationship between Armillaria root disease and organic mulches is also presented.

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The genetic diversity of Taphrina wiesneri causing witches' broom and their distribution across Japan was investigated using PCR-RFLP analysis of the rDNA IGS1 region. Restriction endonuclease Hha I generated six different digestion patterns. Although Acc II, Dde I, Hinf I , Mbo I, and ScrF I generated two to five different digestion patterns, genetic variations revealed these endonuclease were all unveiled by Hha I. Then, Hha I was used to characterize up to six distinct IGS1 types (A-F) of T. wiesneri among 111 isolates analyzed. Types A, B, and C were shown to be dominant in the sampled populations. Only one to three isolates of the remaining types, D, E, and F, were found. All IGS1 types were detected from Prunus x yedoensis, which received serious damage by witches' broom in Japan. Type A was detected throughout Japan, whereas type B was detected from Honshu and Shikoku Island. Type C was detected south of Miyagi Prefecture. These results suggest that the geographical distribution varies depending on the IGS1 types.

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The effects of the thinning season and the bucking method on the emergence of Urocerus japonicus adults, which can discolor the wood of conifers, were investigated. Three thinning seasons (November, February or May) and two treatments (bucked to 2 m or non-bucked) were examined at a hinoki cypress Chamaecyparis obtusa plantation. The density of emergence was higher in bucked to 2 m than in non-bucked for both sexes. The density of male emergence was lowest in the November thinning, but there was no significant difference in the density of female emergence among thinning seasons.

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Plants change their cell permeability in response to stresses. Relations between electrolyte leakage and cell death of pine tissues inoculated with pine wood nematodes were examined in cuttings of current-year shoots and 3 year-old seedlings. Abnormal electrolyte leakage and cell death in inoculated cuttings were observed 6 days after inoculation and then, they progressed together with multiplication of nematodes. Remarkable leakage from xylem tissues preceded disappearance of cell nuclei dyed with DAPI. In 3 year-old seedlings, although nematodes in inoculated shoots multiplied 15 days after inoculation, abnormal leakage wasn't observed till 20 days. And the leakage suddenly occurred after 30 days in inoculated current-year shoots where cell nuclei dyed with DAPI almost disappeared. So, the pattern of electrolyte leakage from pine tissues inoculated with pine wood nematodes was different between two experiments. Only inoculated branches wilted in these seedlings, so that it was suggested that the pattern of the leakage was different because of delay of the disease development.

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