Olive leachates affect germination of Colletotrichum godetiae conidia and the development of appressoria

The effects of nutrients and microorganisms from olive carpospheres on germination of conidia and the development of appressoria of Colletotrichum godetiae were investigated. The final germination ratio was the result of a dynamic equilibrium between the positive action of nutrients and the negative competition of indigenous microorganisms. In contrast, formation of appressoria was greatly increased by microorganisms and reduced by nutrients. Removal of the microbial fraction from olive leachates rich in natural nutrients amplified the vegetative phase after conidium germination, resulting in increased germtube length, and delayed and reduced production of appressoria. Three exogenous nutrients (sucrose, asparagine and glycine) increased germination of conidia and reduced the formation of appressoria. These results provide evidence that nutrients and microorganisms of the olive carposphere play important roles in the infection processes of C. godetiae. Since appressoria are necessary for successful host infection, microorganisms may favour the penetration of C. godetiae by stimulating the production of appressoria, reducing saprophyitic pre-infectional mycelial growth and reducing duration of the critical moist period required for host penetration.