Kyushu Plant Protection Research

During the early development of leaf mold on eggplants caused by Mycbvellosiella nattrassii, the proportion of diseased leaves towards the outer part of the greenhouse was higher than in the center. On diseased leaves, many secondary lesions appeared 20-30 days after the first lesions At the same time, the first lesion appeared on other leaves. As a result, there was an increase in the proportion of diseased leaves. Chemical control carried out twice during early development reduced the proportion of diseased leaves to less than 5% after 45 days.

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A virus-like disease of chrysanthemums occurs in Shizuoka prefecture, Japan. Symptoms of the disease include foliar necrosis and necrotic streaks on the stems. A pathogen isolated from diseased plants was transmitted by Frankliniella occidentalis. The pathogen reacted with Tomato spoted wilt virus (TSWV) antiserum in western blots in which a protein the same size as the TSWV nucleocapsid protein (NP) was detected. The pathogen had a broad host range, systemically infecting 23 species from 7 families out of 39 species from 11 families tested. An electron microscopy study of the pathogen using ultrathin sections of systemically infected Nicotiana rustica leaves revealed clusters of spherical particles 87 nm in diameter within cisternae of the endoplasmic reticulum and filamentous inclusions in the cytoplasm of infected cells. The NP amino acid sequence of the pathogen shared 97.7% identity with that of TSWV. From these results, the pathogen was identified as TSWV. A wide range of susceptibility to TSWV was found in chrysanthemum cultivars, and susceptibility varied greatly depending on the virus isolate.

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We have isolated two ice nucleation-active bacteria, Pseudomonas sp. (INAP) and Xanthomonas sp. (INAX), from tea fields where bacterial shoot blight disease was caused by Pseudomonas syringae pv. theae (P.s.t.). Seasonal population dynamics of P.s.t., INAP and INAX on the phyllosphere were investigated. A major ice nucleation-active bacterium was INAX, which was isolated from 90% of investigated tea fields. On the phyllosphere, the INAX population dynamics were not synchronized with P.s.t. population dynamics, and the INAX population increased during summer in mature tea fields. INAX was also detected in disease lesions with P.s.t..

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The apple snail, Pomacea canaliculata, is an important rice pest in South Japan. It is often found buried in the soils of paddy fields. The daily periodicity of burrowing and the factors affecting this behavior were investigated in rain-free experimental plots (each 2 m² in area) in semi-field conditions. The snails revealed clear daily periodicity in their burrowing during summer. Many snails were buried in the soil in daytime (peak; 9 a.m. to 3 p.m.) and emerged from the soil at night (peak ; 9 p.m. to 3 a.m.) . The proportion of snails buried was significantly larger when water depth in the plots was shallower, even when the depth was still sufficient to cover the shell. In the case of female snails there was a clear tendency for more to be buried when they had not fed, but this did not apply to male adults and juveniles. High water temperature (more than 35°C) increased the burrowing by male adults and almost all males burrowed into the soil at nearly 40 °C. On the other hand, high water temperature did not increase the proportion of burrowing snails for female adults and juveniles. Based on these observations. 0-40% of adult snails and 10-60% of juveniles are expected to be buried in paddy fields by day in the summer when the water depth is 4-6 cm at a water temperature not exceeding 35 °C. The snails showed a similar daily periodicity in late autumn, but seemed to emerge from the soil earlier in late afternoon before the water temperature had decreased, than snails in summer. The proportions of snails buried gradually increased as the seasons advanced, and most snails (70-100%) were buried in soil when the water temperature in the morning fell below 10 °C, suggesting that the low water temperature in autumn and winter accelerates burrowing by the snails.

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