Resistance of Strawberry Plants to Colletotrichum fragariae Affected by Environmental Conditions

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Abstract
Strawberry (Fragaria x ananassa) resistance to Colletotrichum fragariae, the causal agent of anthracnose crown rot (a new name proposed for this disease), is influenced by environmental conditions after inoculation. Strawberry plants were inoculated by spraying with conidial suspensions of two C. fragariae isolates, and subsequent disease development was rated on a severity scale of 0 (no symptoms) to 6 (plant dead). Disease severity ratings of plants inoculated with three concentrations of C. fragariae conidia ranging from 1.5 .times. 106 to 6.0 .times. 106 were not sign ificantly different. Overall, plants incubated at a high temperature (35 C) for 48 hr in a dew chamber (relative humidity near 100%) had higher disease severity ratings than comparable plants incubated at 25 or 30 C. In two of three cultivars tested, inoculated plants maintained in a greenhouse at 32 C after the dew chamber incubation period developed more severe disease symptoms than similar plants held in a greenhouse at 25 C.