Conidial germination and appressorium formation of Colletotrichum coccodes on tomato foliage

Conidial germination and infection processes of Colletotrichum coccodes were quantified on foliage of processing tomatoes (Lycopersicon esculentum Mill.). The abaxial surface of two apposing terminal leaflets removed from a fully expanded leaf at the 4th to 5th node was inoculated with 10-mu l droplets of C. coccodes conidial suspension. Leaflets were incubated for 2 to 24 h in 2-h intervals at 25 degrees C under high relative humidity. Explants with the conidial droplet were fixed, cleared, and preserved for microscopic observation. The percentage of germinated conidia and those with unmelanized and melanized appressoria was determined for each leaf disk. Conidial germination increased linearly with time (R-2 = 0.73) (P = 0.001), maximizing (68.3%) 24 h after inoculation. The percentage of germinated conidia with unmelanized appressoria peaked 6 h after inoculation (38.3%). Melanized appressoria formation followed a linear trend (R-2 = 0.74) (P = 0.001), maximizing (62.0%) 24 h after inoculation. Infection vesicles were produced in 2.7% of conidia by 22 h, indicating successful infection.