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Several fungicides used for the control of rice blast disease have been revealed to inhibit melanin biosynthesis in Pyricularia oryzae at the concentration not affecting vegetative growth of the f ungus. 1, 2) The fungicides including tricyclazole [5-methyl-1, 2, 4-triazolo(3, 4-b) benzothiazole] inhibit appressorial penetration probably due to the lack of melanization in appressoria.3) The other modes of action of tricyclazole in rice blast control were reported as inhibition of secondary infection by spores resulting from suppression of spore formation4) and the decrease of spore pathogenicity4) and from the production of antifungal substance in rice plants. " In this paper we studied the effect of tricyclazole on the appressorial penetration of spores of P. oyyzae, formed de novo in the presence of the chemical.Pyricularia oyyzae Cav., P-2 successively cultured on a V-8 juice agar medium" and on rice plants was used. Rice plants (Oryza sativa cv. , Asahi #4) were grown in pots (9 cm in diameter) in a greenhouse at 25+3C under natural day light. To obtain spores formed on the rice leaves treated with tricyclazole, four week-old healthy plants were put in a moist chamber at 27C together with infected plants as an inoculum for 4 days and then treated with the chemical solution (100 ml per pot) using spray gun; spores formed during incubation for inoculation were washed away during the treatment. The plants treated with the chemical solution were dried and placed in a moist chamber at 30C overnight for formation of spores. Spores formed on the leaves treated with tricyclazole and those formed on the V-8 juice agar medium containing the chemical were collected with a brush and washed three times with deionized sterile water containing 200 , age ml streptomycin (DWS) by centrifugation. The spores were incubated on cellulose membrane and penetration from appressoria was observed as described. 3) The spores formed on the V-8 juice agar medium containing tricyclazole at concentrations higher than 0. 5 ug/ml produced hyaline appressoria on the cellulose membrane resembling those produced from spores incubated in the presence of tricyclazole. The hyaline appressoria did not develop infection hyphae from appressoria and failed to penetrate cellulose membrane (Table 1).Spores formed on the leaves sprayed with 100 ug/ml tricyclazole produced hyaline appressoria with no ability to penetrate cellulose membrane ( Table 2). The frequency of appressorial penetration increased with decreasing tricyclazole concentrations used for the leaf treatment.The results presented in this report indicate that tricyclazole moved systemically into spores formed de novo on the rice leaves treated with tricyclazole and on the V-8 juice agar medium containing the chemical and that tricyclazole concentration in the spores should be high enough to inhibit melanin biosynthesis in appressoria produced from the spores and to inhibit appressorial penetration.This mode

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The initiation and propagation of stress corrosion cracking (SCC) of austenitic stainless steels in boiling 35% magnesium chloride solution, with the pH adjusted to 3.0, were investigated electrochemically by separating the crack anode from the cathode. The dissolution current accompanying crack propagation can be measured, by connecting the anode with the cathode through an external electric circuit, and as a result, the distinction between crack initiation and propagation becomes very clear. The passive-active cell of SCC, simulated by keeping the crack anode potential at the potential of the cathode using a potentiostat, prevents the coupled potential from falling during crack propagation step, accelerates the dissolution of crack anode, and reduces the time to failure. For materials and environments which have low susceptibility to SCC, it can clearly be determined whether SCC occurs or not, by comparing the critical potential for crack propagation, not for initiation, with the corrosion potential of the unstressed steel in the environment concerned. If the former is more active than the latter, SCC can occur. The present method was applied to predict SCC in some chemical equipment, and successful results were obtained.