An unknown leaf blight of the tea plant was found in Kagoshima and Shizuoka Prefectures, Japan, in the spring of 1984 and 1985, respectively. The lesions were reddish to greenish brown in color, almost round in shape and zonate. The causal fungus was identified as Ceuthospora lauri (Greville) Greville on the basis of the morphological characteristics and the pathogenicity onto the tea plant. Brown zonate leaf blight was proposed as the common name of the disease. The present fungus was isolated for the first time in Japan.

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A new bacterial disease has been found on trees of chestnut (Castanea crenata Sieb. et Zucc.) at Makino-cho, Shiga Prefecture since 1977. A canker was developed in early May after swelling of the cortex on over-wintered succulent shoots and then bud death without sprouting or as blight on terminal leaves just after sprouting occurred. Small galls with rough surface developed on the shoot, petioles, midrib of leaves and flower clusters in growing season. One hundred and forty-four isolates of pseudomonads were isolated from the canker and gall lesion occurred on twigs of chestnut. By the method of needle prick inoculation, they induced the formation of galls on twigs of chestnut (cv. Tsukuba) which was similar to the symptoms causing by the natural infection. The causal bacterium was classified in Pseudomonas syringae on the basis of laboratory tests, and was closely resemble to the strain of P. syringae pv. eriobotryae, especially to that of C group classified by Dr. Morita. However, the pathogen of chestnut was weakly pathogenic to loquat and formed small galls which begin to drop off from about 8 weeks after inoculation and recovered at 12 weeks, while P. syringae pv. eriobotryae caused necrotic reaction without gall formation on chestnut trees. Therefore, the present isolates were distinguishable from. P. syringae pv. eriobotryae in pathogenicity and should be a new pathovar of P. syringae. The name Pseudomonas syringae pv. castaneae pv. nov. is proposed and the strain C3 (ICMP 9419, NIAES 2088) was designated as the pathotype strain.

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The infection process of sugar beet flowers and seed balls by Colletotrichum dematium f. spinaciae was studied using light microscope and scanning electron microscope. When infection occurred at early stage of flowering, germ tubes produced appressoria and subsequently infection pegs penetrated the cuticle 3∼4 days after inoculation. Mycelia spread both inter- and intracellularly. Infected cells eventually collapsed, and lesions became visible about 5 days after inoculation. Mycelia were found not only on the surface of blackened seed caps or pericarps, but also in the inner space of the pericarp. In severe infection, mycelia also found between the seed coats and cotyledons. When infection occurred at the late flowering stage, mycelia were frequently observed on the seed surface, but less frequently inside the seed balls. These hyphae were found in the periphery of the apical pore or inside the seed coat. The results indicate that this pathogen is seed-borne.

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Many isolates belonging to the genus Phomopsis were obtained from the concave rot of melon fruit, Cucumis melo, a new postharvest disease. They were divided into four groups of A, B, C and D according to their cultural characters on PSA. Several representative isolates selected from each type of isolates showed clear pathogenicity to melon fruits. Morphologically, isolates were divided into two groups; one having shorter β-conidia and containing colony groups of A and B, and the other having longer β-conidia and containing colony groups C and D. Some isolates of the former group produced perithecial stage on PSA and also on water agar plate containing a fragment of melon fruit. A new variety of Diaporthe melonis Beraha et O'Brien, D. melonis var, brevistylospora Kobayashi et Ohsawa was proposed for the fungus. Although the isolates of the latter did not produce any perithecia on artificial media mentioned above, these were identified as the conidial stage of Diaporthe melonis Beraha et O'Brien var. melonis, Phomopsis cucurbitae McKeen sensu Behara et O'Brien.

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Polyclonal antibody (PoAb) and three monoclonal antibodies (MoAbs), 1C2, 1C9 and 1E2, against tobacco necrotic dwarf virus (TNDV), were produced and their serological characteristics were investigated. Results of antigen adsorption indirect ELISA (AAI-ELISA) by PoAb and MoAbs suggested that TNDV was serologically closely related to potato leafroll virus (PLRV), but far related to beet western yellow virus (BWYV). For detection of TNDV in crude saps, the clones, 1C2 and 1C9 were effective in indirect double antibody sandwich ELISA (IDAS-ELISA) and 1E2 was effective in double antibody sandwich ELISA (DAS-ELISA). These three MoAbs could differentiate PLRV from BWYV when anti-PLRV PoAb was used for trapping antibody in IDAS-ELISA and 1E2 also did in DAS-ELISA.

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A bacterial canker disease of kiwifruit (Actinidia chinensis) has been observed in Shizuoka Prefecture, Japan. Symptoms appear on trunks, leaders and over-wintering canes from late winter to early spring as cankers and cracks, when red-rusty brown bacterial ooze exudes from these lesions or from apparently healthy buds, leaf scars, lenticels and joints of trunks, leaders and canes. In late spring, brown water-soaked lesions with halos appear on leaves, and wilt or blight of vigorous canes and flower buds is also observed. A characteristic white bacterium is consistently isolated from the affected tissues, isolates of which reproduce typical symptoms on kiwifruit and Actinidia arguta when inoculated either with or without wounding in spring and winter. Kiwifruit leaves are most susceptible to the pathogen just before maturation and are less susceptible at younger and older stages. Climatic conditions such as low temperatures, strong winds, and heavy rainfall appear to promote the disease. Applications of streptomycin, kasugamycin or inorganic copper formulations reduced disease development on leaves.

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Bacterial canker of Kiwifruit (Actinidia chinensis) has recently been reported in Japan. The causal pathogen is classified in Pseudomonas syringae on the basis of laboratory tests and is similar to, but not identical with, P. syringae pv. morsprunorum. In inoculated kiwifruit, the pathogen from kiwifruit reproduces the characteristic canker and leaf spot symptoms. P. syringae pv. syringae and P. syringae pv. morsprunorum are only weakly virulent to kiwifruit. The pathogen from kiwifruit is weakly pathogenic to peach and Japanese apricot, but not to 24 other plant species tested. The pathogen is considered to be a pathovar of P. syringae and the name P. syringae pv. actinidiae pv. nov. is proposed. Strain Kw-11 (ICMP 9617) is designated as the pathotype strain.

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When potted plants of cv. St. George infected with grapevine fanleaf virus (GFV) were kept under the temperature conditions of 28/23C (day/night) or 20/17C, the newly developed leaves did not show typical symptoms of GFV such as wide petiole sinus, asymmetrical blade shape and leaf blades assuming the shape of a fan until 50 days after sprouting. The denticulation of the margins of the leaf blades on infected plants also showed almost no difference from those of healthy plants during the 50 days. However, the middle lobe cusps of these leaves on the infected plants were very acute after the above incubation period, and clearly different from those of healthy plants. The symptoms appeared faster under the higher temperature condition of 28/23C than under the lower temperature condition of 20/17C. Sharpening ratios for the cusps of the middle lobes of infected and healthy leaves were compared. Infected plants were indicated by ratios exceeding 2.6 in the 50 days period. On the other hand, healthy plants were indicated by ratios less than 2.6. A sharpening ratio of 2.6 was converted into a value of 42.4 degrees for the angle of the middle lobe cusp of a leaf. Grapevine fanleaf can be rapidly diagnosed in cv. St. George within a period of 50 days after sprouting on the basis of the following criteria. At temperatures of 28/23C, values below 42.4 degrees for the angle of the middle lobe cusps of three successive leaves from the fourth to the sixth in leaf order from the base of a shoot indicate infection with grapevine fanleaf virus. The measurement of this angle is easily made by using a magnifying glass with a V mark of 42.4 degrees, or with the naked eye.

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We confirmed that a wilt of adzuki bean (Vigna angularis (Willd.) Ohwi & Ohashi) in Hokkaido is caused by a new forma specialis of Fusarium oxysporum reported by Kitazawa and Yanagita as Fusarium oxysporum f. sp. adzukicola. We also suggested “Adzuki icho-byo” as the Japanese name of adzuki bean wilt caused by Fusarium oxysporum f. sp. adzukicola. The susceptibility of adzuki bean cultivars and lines to adzuki bean wilt was determined in greenhouse and field tests. For greenhouse tests, the roots of 7- to 10-day-old seedlings grown in sterilized vermiculite were dipped for about 1hr in a suspension of spores of Fusarium oxysporum f. sp. adzukicola (10⁶ microconidia/ml) and the seedlings were then transplanted into pots filled with sterilized soil. Plants for these tests were grown at temperatures between 18∼33C. Initial symptoms on susceptible plants appeared about 10∼14 days after inoculation. The typical symptoms observed in the greenhouse test were similar to those observed on plants grown in fields. The response of 22 cultivars and lines to eight isolates of F. o. f. sp. adzukicola resulted in the identification of three races of the fungus. The reaction of cultivars in field tests were similar to those for race 3 in greenhouse tests. It was concluded that screening of adzuki bean germ plasm in greenhouse tests is effective in selecting for resistance.

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A susceptible melon cultivar Earl's (Cucumis melo L. var. reticulatus) reacted to cucumber mosaic virus (CMV) by producing diffuse chlorotic spots on inoculated leaves, which supported a high level of virus multiplication. By contrast, the inoculated leaves of a resistant cultivar Kohimeuri (C. melo L. var. makuwa), produced smaller chlorotic spots, which did not enlarge even at late stage of infection, and the leaf extracts had much lower infectivity than those of Earl's. The fluorescent antibody staining of epidermis or sections from inoculated leaves showed that the virus infected cells in Earl's were increased with time after inoculation, while those in Kohimeuri were localized within a small leaf area. The virus multiplication and distribution in Kohimeuri leaves, however, were markedly enhanced in the presence of actinomycin D. When the mesophyll protoplasts isolated from each cultivar were inoculated with CMV-RNA by the electro-transfection method, similar pattern of virus multiplication was obtained. These results suggested that this type of resistance operates mainly at the intercellular level of response after virus infection.

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[in Japanese]

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