Annual Report of The Kansai Plant Protection Society

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A purification procedure has been devised for a highly potent inhibitor of virus infection occurring in seeds of Dianthus barbatus L. The seeds were homogenized in 0.1M phosphate buffer, pH 7.0 (neutral PB), and centrifuged at low speed (at 10,000xg for 20 minutes). The supernatant was chromatographed on a Sephadex G-100 column which had been equilibrated with neutral PB. The active fraction was mixed with 66 g of ammonium sulfate per 100 ml of the solution with stirring. The resultant precipitation was dissolved in neutral PB followed by centrifugation. The supernatant was chromatographed on a Bio-Gel P-60 column, and anti-viral activity was observed in the high molecular-weight material fraction. The active fraction was chromatographed on a DEAE or ECTEOLA cellulose column which had been equilibrated with neutral PB, and the anti-viral activity was observed on the non-adsorbed fraction. Finally, the active fraction was chromatographed on a CM cellulose column which had been equilibrated with 0.05M phosphate buffer, pH 6.5. The anti-viral activity was observed on both the non-adsorbed and adsorbed fractions. The obtained inhibitor was thermo-labile. Se-phadex G-100 gel filtration experiments suggested that the inhibitor's molecular weight ranges between 20,000 and 40,000.

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Influences of moisture, electric conductivity (EC), and pH of soils on the incidence of damping-off of spinach seedlings caused by Pythium aphanidermatum and P. paroecandrum were studied. The incidence of damping-off increased considerably at high soil moisture, especially with more than 40% of soil water content. The incidence was not significantly different between upland fields and drained rice paddy fields where spinach had been cultivated for more than 3 consecutive years. A negative correlation was found between the incidence of damping-off and EC values of soils (r=-0.5094** in upland fields and r=-0.3601* in drained paddy fields), and also between plant height and EC values (r=-0.6491**). Hyphal growth of the pathogen on corn-meal agar was maximal at pH 6.6-7.0, decreased at pH 4.0, but not considerable at pH 9.0. Soil pH of spinach fields ranged from 5.5 to 7.5, and most were very close to the above optimum pH. However, no significant correlation was found between the incidence of damping-off and soil pH. The young seedlings were most sensitive to the disease and became resistant with the seedling age. Damping-off was severe within two weeks after sowing.

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Efficacy of validamycin A (VM-A) for several sclerotial diseases was studied in vitro and in vivo. These diseases were caused by several sclerotial fungi such as Rhizoctonia solani I A, Rhizoctonia solani III B, Rhizoctonia oryzae, Sclerotium fumigatum, Sclerotium oryzae-sativae and Sclerotium hydrophilum. In vitro tests indicated that all these fungi were sensitive to VM-A and showed abnormalhyphal growth at 10 ppm VM-A after 1 to 2 days of incubation. Each sclerotial disease could be induced in rice plants by inoculation of mycelial blocks of each fungus at 26 to 32°C. In curative condition, VM-A (7.5 ppm) was effective for all sheath blight-like diseases except brown sclerotial disease by S. oryzae-sativae and brown sheath blight by R. solani III B, for which 60 ppm and 30 ppm VM-A were required, respectively. In protective condition 15-60 ppm was effective for these sclerotial diseases including rice sheath blight disease.

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This study examined the effect of different bactericides and fungicides on oospore germination of Aphanomyces iridis. The results obtained are as follows. (1) Oospores can be divided into morphologically complete and incomplete oospores under a light microscope. (2) Both corn meal decoction (CMD) and FOWLES's defined liquid (FDL) media are suitable for producing many complete oospores. (3) Complete oospores with high germinability can be obtained after growing the fungus on either CMD or FDL medium for 2 weeks at 25°C. (4) Optimum temperature and pH for oospore germination are 25°C and about 6.4, respectively. (5) No inhibitory action of oospore germination is usually seen when chloramphenicol, streptomycin sulfate and vancomycin are used at concentrations up to 100, 80 and 400 ppm, respectively, although the latter two are both sometimes inhibitory at 20-40 and 100 ppm. (6) Amphotericin B, benomyl and iprodione inhibit oospore germination at concentrations higher than 5, 0.5 and 50-100 ppm, respectively. Benomyl is highly inhibitory even at 0.5-1 ppm. Metalaxyl inhibits at the intermediate concentrations used and thiophanatemethyl inhibits at the concentrations higher than 10-50 ppm.

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