Twenty-three isolates of Verticillium sp. were obtained from cultivated field soils inoculated with Rhizoctonia solani 5 times at 2 weeks intervals. These 23 isolates had different levels of suppressiveness to damping-off of sugar beet caused by R. solani AG2-2-IV in pot tests. Two isolates (HV8 and HV10) were selected as the most effective. In pot tests, the isolates were more effective in reducing damping-off and the colonization of sugar beet seeds by R. solani with higher concentrations of isolate-infested wheat-bran vermiculite Czapek-Dox culture. An almost similar level of control was attained by applying 5% wheat-bran vermiculite Czapek-Dox culture of the isolates in the total soil and 40ppm of PCNB. Incidence of root rot was reduced to 45% of the untreated control when Verticillium sp. was applied once to field soil near the tap root of sugar beet one day before inoculation with R. solani (July 9th, 1996). Incidence was reduced to 70% when two more applications were added to nursery soil (April 15th, 1996) and to the planting hole (May 27th, 1996). Light microscopic observation showed that the Verticillium sp. isolates penetrated only living R. solani hyphae stained with 2-(4-lodophenyl)-3-(4-nitrophenyl)-5-phenyl-2H-tetrazolium chloride, and infected host cells later died. These isolates were identified as V. biguttatum on the basis of morphology and temperature responses.

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Infection process by Mycovellosiella nattrassi, the causal agent of leaf mold of eggplant, was histologically observed on host and nonhost plants using scanning electron and bright field microscopy. The fungus penetrated the leaf tissues through stomata. After penetration, the hyphae ramified and grew in the intercellular spaces of the spongy mesophyll cells. After vigorous growth in the spongy cells, aerial hyphae grew through stomata onto the leaf surface. In a comparison of the infection process between the adaxial and abaxial sides of the leaf after artificial inoculation, infection was more frequent on the abaxial side than adaxial. Aerial hyphae also developed more rapidly through stomata on the abaxial side. As one of the host responses, cytoplasm became granulated in the palisade and epidermal cells. On a nonhost, such as tomato and sweet pepper, the fungus also penetrated in the same mode as in eggplants; however, the growth of hyphae on nonhost plants was poorer than that on eggplants.

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To establish low chemical input disease protection for rice plants, we designed a seed disinfection method using hot water to control seed-borne fungal and bacterial rice diseases. In this study, three sets of 10-kg weight seeds infested with Fusarium moniliforme, Pyricularia oryzae or Pseudomonas plantarii were immersed in 200l of hot water at 58 or 60°C for 10 to 20min using an experimental machine that could accurately maintain the water temperature (±0.1°C). The occurrence of each disease and the rate of seedling emergence in the nursery beds were observed after the hot water treatment. Hot water immersion was just as effective as conventional chemical seed disinfection in controlling the diseases. In a germination test, more than 90% seed germination was obtained with 20min at 58°C or 15min at 60°C for eight nonglutinous rice cultivars, but not for three glutinous rice cultivars. From these results, hot water immersion for seed disinfection is a promising method compared to conventional chemical seed disinfection methods.

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During the years 1997-1999, a rot disease on mature fruit of persimmon (Diospyros kaki) occurred in several areas in Gifu Prefecture where persimmon is extensively produced. The disease was characterized by rotting from the fruit apex or base. From the results of fungal isolation and tests of their pathogenicity, the rotting was caused by two species of the fungal genus Pestalotiopsis. One was identified as Pestalotiopsis longiseta (Spegazzini) Dai et Kobayashi and the other as P. foedans (Saccardo et Ellis) Steyaert, on the basis of their morphological and cultural characteristics. These pathogens could invade through cavities of the fruit apex or base, producing a black discoloration or rot. Losses due to the fruit rot were effectively reduced by three sprays of the fungicide iminoctadine-albesilate from August to October with occasional sprays right after strong winds and heavy rain.

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In February 1999, cineraria (Senecio×hybridus) plants with necrotic ring spot were found in Okayama Prefecture, Japan. A spherical virus with a diameter of ca. 85∼120nm was isolated. The virus infected seven plant species of four families after mechanical inoculation. In serological tests, the virus was closely related to Impatiens necrotic spot virus (INSV). In RT-PCR with INSV-specific primers, a fragment of about 900bp was amplified. The fragment had a high degree of nucleotide sequence homology with the S RNA of INSV. Based on these results, the virus isolated from cineraria was identified as INSV. This is the first report of INSV on cineraria in Japan.

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Cucumber plants (Cucumis sativus) with necrotic spots, yellowing and mosaic symptoms were found in Kochi Prefecture, Japan in 1995. The causal agent was identified as Melon yellow spot virus (MYSV) on the basis of host reactions, stability in crude sap, particle morphology, transmission by Thrips palmi, serological relationships and the identity of amino acid sequence of the N protein. This is the first report of the occurrence of MYSV on cucumber, and the name “potted wilt”s was proposed for the disease.

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