Yoshio Hisada

Systemic movement in cucumber plants and control of cucumber gray mould by a new fungicide, S-7131

Carbon-14-labelled S-7131 (N-(3′,5′-dichlorophenyl)-1,2-dimethylcyclopropane-1,2-dicarboximide) penetrated into the treated leaves of cucumber plants, moved to the stem and was then translocated both upwards and slightly downwards. Also through roots the fungicide was readily taken up and translocated to aerial parts. Autoradiographs showed that S-7131 had a tendency to accumulate at the leaf margin. In experiments with cucumber plants bearing flowers and fruits it was shown that S-7131 hardly moved from foliage to flowers and fruits. TLC analysis of radioactive extracts showed that S-7131 moved within plants in the unaltered form. Bioassay tests confirmed that systemic movement of S-7131 contributed to its high efficacy in disease control.

Synthesis and Fungicidal Activity of 1-(α-tert-Butylcinnamoyl)imidazoles

Several 1-(α-tert-butylcinnamoyl)imidazoles were prepared to examine their fungicidal activity. The (Z)-4-chlorocinnamoyl derivative was prepared from (anti)-2-tert-butyl-3-(4-chlorophenyl)-3-hydroxypropanoic acid by treating with 1,1′-carbonyldiimidazole and a subsequent β-elimination reaction at an elevated temperature. The (Z)-isomer of the 4-chlorocinnamoyl derivative showed good fungicidal activity against Erysiphe graminis and Botrytis cinerea in pot tests, whereas the corresponding (E)-isomer derived from the (Z)-isomer through photoisomerization was much less active.

Nature of Procymidone-Tolerant Botrytis Cinerea Strains Obtained in Vitro

Tolerance of plant pathogens to fungicides was not a serious problem when mainly non-systemic conventional fungicides were used. These fungicides have been called “multi-site inhibitors” because they non-selectively inhibit several biologically important functions of living fungal cells. The nature of their fungitoxic mechanisms implies that there is little possibility for the development of tolerant mutants because mutation of a single gene cannot overcome the lethal effect of their multisite activity. On the other hand, we have seen emergence of tolerant pathogens with the recently introduced systemic fungicides. Since these systemic fungicides can easily penetrate into plant tissues, they must be selectively toxic to pathogens at concentrations that do not produce phytotoxic effects. Therefore, systemic fungicides have been understood to be “specific-site inhibitors” as they affect biochemically restricted regions of fungal cells. This intrinsic nature of systemic fungicides accelerated the selection of the fungicide-tolerant pathogens that appeared through mutation of a single gene.

Quantitative structure-activity relationships for antifungal 3-(3,5-dichlorophenyl)-2,4-imidazolidinediones

The antifungal activity of 441-acyl derivatives of 3-(3,5-dichlorophenyl)-2,4-imidazol- idinedione against Botrytis cinerea, and of 10 1-sulfonyl compounds against Aiternaria kikuchi- ana were assayed by the agar medium dilution method. The structure-activity relationships for the substituents of the acyl and sulfonyl moieties were analyzed with such physicochemical parameters as hydrophobic π, inductive electronic σ1, and steric E′cs and B1 values by multiple regression. The activity of the acyl derivatives against B. cinerea was related parabolically to the hydrophobicity of the substituents. The stronger the electron-donating power, the larger the overall steric bulkiness, and the smaller the minimum width in the direction perpendicular to the bond axis of the substituents, the greater was the activity. The activity of the sulfonyl derivatives against A. kikuciana was related only to the hydrophobicity of the substituents.