Studies on the infection strategy as the blossom pathogen on the Japanese cedar twig blight

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The primary infection court for the onset of twig blight of Japanese cedar, Sugi (Cryptomeria japonica), caused by the pathogen Stromatinia cryptomeriae, is the male strobilus. It was hypothesized that the male strobili provide a favorable environment for ascospore germination and hyphal growth. Consequently, the roles of pollen, water-retention and micro-flora in germination of ascospores in the strobili were investigated. In the first 6 hours after ascospores of S. cryptomeriae were released onto various aqueous suspensions of cedar pollen, no ascospore germination occurred in any treatment. However, at 12 hours all ascospores had germinated in all suspensions containing cedar pollen. The levels ascospore germination increased in proportion to the concentration of pollen in the suspension. Whereas a few ascospores germinated in sterilized water free of pollen, no ascospores germinated in the absence of water. The existence of a saccaride and an amino acid was confirmed by the an analytical study of the extracts in Japanese cedar pollen. These results show that water is indispensable in germination of the ascospores and that cedar pollen grains promote the germination. Male strobili at different stages of development were collected from infected trees. Pestalotiopsis sp., Phoma sp. and Cladosporium sp. were most frequently isolated from the immature strobili and appear to be endophytes. The fungi most frequently isolated from mature male strobili were Pestalotiopsis sp., Phoma sp. snd S.cryptomeriae. This observation indicates that the twig blight pathogen is able to coexist with these other fungi however, it is unclear whether they assist in its invasion of the strobili or stand against its invasion (antagonism).