INHIBITORS OF APPRESSORIUM FORMATION IN MAGNAPORTHE-GRISEA - A NEW APPROACH TO CONTROL RICE BLAST DISEASE

Fungi were screened for the production of inhibitors of appressorium f ormation in germinating conidiospores of Magnaporthe grisea on inducti ve and non-inductive surfaces. Bioactivity-guided isolation yielded gl isoprenins A, C, D and E from Gliocladium roseum and oleic acid from t hree fungi. The glisoprenins were active only on a hydrophobic surface , whereas oleic acid inhibited appressorium formation on a hydrophilic surface when 1,16-hexadecanediol, but not (4-chlorophenylthio)adenosi ne-3',5'-monophosphate, was used as inducer. The inhibition by glisopr enins could be reversed competitively by 1,2-dioctanoylglycerol but no t by 1-oleoyl-2-acetyl-glycerol, both effective activators of protein kinase C in mammalian cells. Other mono-unsaturated fatty acids also i nhibited appressorium formation. The corresponding methyl esters were inactive. The results agree with previous findings that at least two s ignal-transducing pathways are involved in appressorium formation. In addition, the differences observed between fungal signalling via PKC a nd the pathway used in mammalian cells could be used for the search fo r new and selective fungicides for rice blast disease. (C) 1998 Societ y of Chemical Industry.