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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 Colletotrichum coccodes were determined by inoculating plants with C. coccodes (5.0 × 10⁵ conidia per ml) and keeping them in a dew chamber for 0, 4, 8, 12, 16, 20, or 24 h of wetting at 15, 20, or 25°C. One week after inoculation, leaf disks were placed on the surface of an amended medium on which colonies of C. coccodes were compact and easily identified, and severity of infection was quantified after 4, 6, and 8 days. There was no infection of plants incubated at 15°C, while plants kept at 20 or 25°C had increasing numbers of colonies when leaf wetness duration was extended beyond 12 and 8 h, respectively. Leaf position had a significant effect, with leaves tending to increase in susceptibility as they age. After 24 h of leaf wetness at 25°C, the mean number of colonies per leaf disk from top, middle, and bottom leaves was 23.8, 29.0, and 34.0, respectively.