Advantageous properties of a new fungicide, isofetamid.

The fungicidal properties of a new fungicide, isofetamid, were examined to assess its antifungal spectrum, mode of action, and effects on the infection process of Botrytis cinerea. Additionally, we investigated its fungicidal activity against isolates of B. cinerea resistant to existing fungicides. In mycelial growth inhibition tests, isofetamid exhibited excellent fungicidal activity against ascomycetes but showed no activity against basidiomycetes and oomycetes. Respiratory enzyme assay using mitochondria revealed that isofetamid inhibited succinate dehydrogenase activity prepared from B. cinerea and other ascomycetes fungi used in the study. On the other hand, the activity of mitochondria prepared from Pythium, potato and rat were not inhibited. Isofetamid inhibited also many stages of the infection processes in B. cinerea. Furthermore, it exhibited high fungicidal activity against B. cinerea isolates that were resistant to existing fungicides.

At Least Five Major Genes Are Involved in the Avirulence of an Eleusine Isolate of Pyricularia oryzae on Common Wheat.

Pyricularia oryzae is composed of pathotypes that show host specificity at the plant genus level. To elucidate the genetic mechanisms of the incompatibility between the Eleusine pathotype (pathogenic on finger millet) and common wheat, an Eleusine isolate (MZ5-1-6) was crossed with a Triticum isolate (Br48) pathogenic on wheat, and resulting F1 cultures were sprayed onto common wheat cultivars Hope, Norin 4 (N4), and Chinese Spring (CS). On Hope, avirulent and virulent cultures segregated in a 3:1 ratio, suggesting that two avirulence genes are involved. They were tentatively designated as eA1 and eA2. On N4 and CS, the segregation ratio was not significantly deviated from the 7:1, 15:1, or 31:1 ratios, suggesting that three or more genes are involved. A comparative analysis of the segregation patterns suggested that two of these genes were eA1 and eA2. A complementation test indicated that the third gene (tentatively designated as eA3) was the Ao9 type of the PWT3 gene controlling the avirulence of Avena and Lolium isolates on wheat. The fourth gene (tentatively designated as eA4) was detected by backcrossing 200R72, an F1 culture lacking eA1, eA2, and eA3, with Br48. Comparative analyses of phenotypes and the presence and/or absence of molecular markers in the F1 population revealed that some cultures were avirulent on N4/CS in spite of lacking eA1, eA2, eA3, and eA4, indicating the presence of the fifth gene (tentatively designated as eA5). Taken together, we conclude that at least five avirulence genes are involved in the incompatibility between MZ5-1-6 and N4/CS.