CHEMICAL SIGNALS FROM AVOCADO SURFACE WAX TRIGGER GERMINATION AND APPRESSORIUM FORMATION IN COLLETOTRICHUM-GLOEOSPORIOIDES

The surface wax of the host, avocado (Persea americana) fruit, induced germination and appressorium formation in the spores of Colletotrichu m gloeosporioides. Waxes from nonhost plants did not induce appressori um formation in this fungus, and avocado wax did not induce appressori um formation in most Colletotrichum species that infect other hosts. B ioassays of the thin-layer chromatographic fractions of the avocado wa x showed that the fatty alcohol fraction was the main appressorium-ind ucing component. Testing of authentic n-C8 to n-C32 fatty alcohols rev ealed that C24 and longer-chain alcohols induced appressorium formatio n. Gas-liquid chromatography/mass spectrometry analysis of free fatty alcohols revealed that avocado wax contains a high content of very lon g chains. Waxes from nonhost plants containing an even higher content of the very long-chain alcohols did not induce appressorium formation. Waxes from nonhost plants strongly inhibited appressorium induction b y avocado wax. Thus, a favorable balance between appressorium-inducing very long-chain fatty alcohols and the absence of inhibitors allows t he fungus to use the host surface wax to trigger germination and diffe rentiation of infection structures in the pathogen.