Abstract
In the course of our research work for a novel systemic fungicide to control rice sheath blight disease caused by Rhizoctonia solani, various derivatives having amide linkage, especially benzanilide derivatives were synthesized for biological screening. Trifluoromethyl at the ortho position of the acid moiety of benzanilide was selected as the most favorable substituent with a certain level of steric bulk and lipoid solubility. Alkoxy groups introduced at the meta position of the aniline moiety enhanced the fungitoxic activity. Ultimately, flutolanil (α, α, α-trifluoro-3′-isopropoxy-2-toluanilide) was selected as the most potent compound for our purpose. Flutolanil is the first registered fungicide able to control rice sheath blight with application of granules into paddy water as well as foliar spray application in Japan. Approximately 2ppm of flutolanil in rice leaf sheaths contributed to about 80% suppression of the disease development by inhibiting hyphal growth, infection-cushion formation and penetration from infection cushion of R. solani on leaf sheaths. In paddy fields, flutolanil showed the best performance when applied into paddy water during the horizontal development of the disease or when applied as a foliar spray once or twice at appropriate timing. Biochemical mode of action of flutolanil seems to be inhibition of a succinate dehydrogenase complex, an important enzyme complex in the respiratory chain of basidiomycetous fungi but not of fungi in other classes. Toxicological and metabolic studies revealed the character of flutolanil highly safe to mammalians and environment.
