Deposition and adhesion of spores of Fusarium culmorum on hydrilla

Fusarium culmorum is a pathogen of the submerged aquatic weed Hydrilla verticillata. The deposition and attachment of macroconidia and chlamydospores of F. culmorum in water was investigated using assays with glass slides and hydrilla shoots. The number of spores deposited on leaves along the length of hydrilla shoots in test tubes did not vary significantly with depth. Macroconidia and chlamydospores deposited on the leaf did not become attached to the surface for several hours. Two-week-old macroconidia required 3 h for attachment and 6-week-old chlamydospores required 7 h. Pretreatment of macroconidia in hydrilla extract induced production of an adhesive substance from the tips of: the macroconidia, which attached to glass slides and hydrilla leaves. The adhesive substance was induced after incubation for 1 min in hydrilla extract, and the adhesive capacity declined after 20 min of incubation. Macroconidia that adhered to glass slides began to break free after 3 h. Co-incubation of macroconidia in hydrilla extract and the lectin concanavalin A prevented adhesion of the macroconidia. Deposition and attachment of spores in the hydrilla - F. culmorum pathosystem is complex and must be understood in relation to dispersal of spores in water.