Causal Factors and Control of the Necrotic Disorder of Berries in 'Muscat of Alexandria' Grape

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The necrotic disorder of grape berries, so called 'Shukuka-byo' in Japanese, has been considered due to physiological breakdown, but prevention of this disorder is yet obscure. Authors supposed that it should be a vascular disease infected by unknown organisms because of its first browning symptom appeared on vascular bundles, and preventive effectiveness of some antibiotic treatments.Numerous oval to spherical granules were observed in sieve elements and adjacent parenchymatous cells at receptacles and the basal portion of suffered berries, but rare in healthy berries through SEM. The granules were mostly ca. 0.5-1.0 mum of diameter, but some were smaller and others larger, and some were smooth in its surface but others rough. Rough granules of 0.2-2.0 mum were observed in the clonies on the medium inoculated with tissues, and smooth granules of 0.2-1.8 mum were also observed in the precipitated fraction of centrifuged juice of suffered berries. But we could not find any microorganisms through TEM, except some orbicular structures of 0.2-1.0 mum without clear membrane and interior, which were supposed to be broken down mitochondria. Xylem sap contained some organism-like granules of 0.05- 0.2 mum with membrane. MLO-like colonies were frequently produced around the tissues of healthy and/or suffered berries and receptacles on the StageII to maturation, but not around the tissues from the tip-cultured grapevines, which were planted in a netted greenhouse protected from leafhoppers and did not show any symptoms of the necrotic disorder. The colonies did not grow any more by its transplanting, and also did not grow through the cellulose films for dialysis laying against the tissues. Nucleic acids were detected from the granules in precipitate fraction after 12,000 centrifugation(G) of liquid culture medium. Pathogenisity of the granules was not elucidated by several inoculation, except a instance of basal treatment to the aseptic cultured cuttings in tubes.