INFLUENCE OF DEW PERIOD AND TEMPERATURE ON FOLIAR INFECTION OF GREENHOUSE-GROWN TOMATO BY COLLETOTRICHUM-COCCODES

Effects of temperature, duration of leaf wetness, and leaf position on foliar infection of greenhouse-grown tomato (cv. Bonnie Best) by Coll etotrichum coccodes were determined by inoculating plants with C. cocc odes (5.0 x 10(5) conidia per ml) and keeping them in a dew chamber fo r 0, 4, 8, 12, 16, 20, or 24 h of wetting at 15, 20, or 25 degrees C. One week after inoculation, leaf disks were placed on the surface of a n amended medium on which colonies of C. coccodes were compact and eas ily identified, and severity of infection was quantified after 4, 6, a nd 8 days. There was no infection of plants incubated at 15 degrees C, while plants kept at 20 or 25 degrees C had increasing numbers of col onies when leaf wetness duration was extended beyond 12 and 8 h, respe ctively. Leaf position had a significant effect, with leaves tending t o increase in susceptibility as they age. After 24 h of leaf wetness a t 25 degrees C, the mean number of colonies per leaf disk from top, mi ddle, and bottom leaves was 23.8, 29.0, and 34.0, respectively.