Abstract
Colletotrichum gloeosporioides, C. coccodes, and C. dematium are responsible for pepper anthracnose and they infect pepper as tissue-specific manner. They form a specialized infection structure, an appressorium, to infect the host. Contacting hard surface induces appressorium formation in these fungi, whereas hydrophobicity of the contact surface does not affect this infection-related differentiation. To investigate the common signal transduction pathways involved in conidial germination and appressorium formation, several pharmacological agents thought to act on critical steps in cAMP- and calcium-dependent signaling pathways were tested. Exogenous addition of cAMP did not alter both differentiations of all 3 anthracnose pathogens tested. Two phosphodiesterase inhibitors, caffeine and isobutylmethylxanthine (IBMX), specifically diminished appressorium formation of C. gloeosporioides and conidial germination of C. dematium. Addition of Ca 2+ specifically reduced appressorium formation of C. coccodes and C. dematium, whereas EGTA (calcium chelator) and neomycin (phospholipase C inhibitor) showed nonspecific inhibitory effects on both developments. Calcium channel blockers and calmodulin antagonists showed species-specific inhibitory effects. These results suggest that calcium/calmodulin-dependent signaling pathway plays an essential role on conidial germination and appressorium formation in pepper anthracnose pathogens.
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