Effects of Ca²⁺/calmodulin mediated signaling on spore germination and appressorium development in Colletotrichum falcatum went

Colletotrichum falcatum Went, the causal agent of red rot of sugarcane produces a specialized infection structure called appressorium, for penetrating the host. Environmental cues like surface hydrophobicity and hardness tend to break the dormancy of the conidia and initiate conidial germination. Conidial attachment is generally stronger on hydrophobic surfaces, while hydrophilic surfaces do not permit conidial attachment of C. falcatum. In vitro studies on conidial germination and appressorium development were made to examine whether the Ca²+/ cal-modulin dependent pathways are involved in appressorium formation in C. falcatum. Effects of calcium chelator (EGTA), calcium channel blocker (methoxy verampamil), calmodulin antagonists (chloropromazine, phenoxy benzamine and W-7) and phospholipase C inhibitor (neomycin) were also examined to see whether they can impair conidial germination and appressorium development. All these chemicals were found to inhibit conidial germination and or appressorium formation in C. falcatum. Chloropromazine and W-7 specifically inhibited appressorium formation at the μM level. Exogenous addition of Ca²⁺ was found to restore the, inhibition of conidial germination and appressorium development by EGTA. These results suggest that the Ca²⁺/calmodulin signal transduction pathway play an important role in the conidial morphogenesis and appressorium development in C. falcatum.