Studies on invasional or importational routes of tree-disease pathogens in East Asia

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Ribosomal DNA sequences of tree-phytoplasmas were analyzed and examined their relationship with closely related East Asian species. 'Candidatus P.ziziphi' was detected in Hovenia witches'-broom in Japan and a privet disease showing dwarf symptoms, and jujube witches'-broom, were found in Korea. All their rDNA sequences were homologous. A species closely related to the Elaeocarpus yellows phytoplasma was detected in Elaeocarpus sylvestris, E.japonicus in Japan. In addition, several other hosts e.g. Pieris taiwanensis, were detected in Taiwan. They showed almost no differences in 16S rDNA. In the ITS domain, the Japanese pathogens were identical, but the Taiwanese pathogens exhibited individual differences. These results suggest that the distribution of the pathogen would take much longer in Taiwan than in Japan.DNA sequences of some gene regions were analyzed on the pathogen of pitch canker disease of pines. Fusarium circinatum isolates examined have completely the same DNA sequence on Histone H3. Maximal Parsimony analyses were conducted on the data set of benA, TEF and IGS. Japanese isolates were divided into two groups. One of them formed one phylogenetically-related group together with most of Korean isolates and a part of American and South African isolates. The rest of Korean, American and South African isolates also formed another phylogenetic group. It was suggested that the pathogen was introduced as a clone into Japan or Korea and gradually became diverged at the individual locations.Plant-quarantine systems in peripheral countries were examined. As for the Zizyphus jujube, there were a few records of importation from South Korea to Japan. As the inspections are made by surface-observation on living-trees, symptomless infections are escapable. We recommend the adaptation of PCR for plant-quarantine.