Studies on life cycle and ecology of spruce rusts in the central mountainous region of Japan

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The spruce rusts, which are known as destructive disease of Picea plants in Europe and North America, have often been recorded to occur in Japan. However, the life cycle and ecology of the causal fungi remain mostly uncertain. In the present study, field surveys, morphological observations and inoculation experiments were carried out to clarify the life cycle and ecology of spruce rust fungi in the central mountainous region of Japan. From field surveys and taxonomic examinations, the rust occurred on P.koyamae and P.shirasawae was identified as Chrysomyxa abietis, and the rust on P.jezoensis var.hondoensis was identified as C.succinea. Additonally, a new Chrysomyxa rust host-alternating between P.polita and Rhododendron dilatatum was found in several locations of the central mountainous region. PCR-RFLP analysis of IGS1 region in rDNA was carried out to clarify the genetic structure of C.succinea populations. Genetic variations were detected in heteroecious populations in Mt.Yastugatake, Fuji 3-gome and Fuji Gotenniwa, whereas there was no genetic diversity in autoecious populations in Fuji 5-gome and Fuji Oniwa. These results suggest that C.succinea may be composed of heteroecious and autoecious populations which are genetically differentiated from each other.