Leaf blotch and stem-end rot caused by Gnomonia comari P. Karst. (anamorph, Zythia fragariae Laibach) were observed in a strawberry fruit production field at Watsonville, CA, in 1996. Z. fragariae has been known for years to attack leaves and cause leaf blotch but this is the first time that the perfect stage, G. comari, was identified and documented to infect fruits and cause stem-end rot in California. Symptoms on leaves included pin-point lesions, brownish to purplish blotches, and characteristic large V-shaped lesions. On the fruit, infection showed more frequently on the calyx. Symptoms on the calyx ranged from small lesions on the sepals to a completely infected calyx that turned necrotic and brittle. Calyx infection was observed on seemingly healthy green and ripe fruits. Infected fruits ripened prematurely and turned pale red to brownish in color. They remained firm but were often invaded by secondary organisms including Botrytis cinerea. When infected leaves and fruits were surface sterilized and incubated under humid condition, perithecia and pycnidia readily developed on the lesions. Ascospores oozed from the tip of the perithecial neck while numerous spores oozed out of the pycnidium. The pathogen was identified as G. comari based on size and morphology of the perithecia, asci, and ascospores (1), and the spores were identified as Z. fragariae based on morphology of the conidia and conidiophores (2). Both the spores and ascospores produced pycnidia and perithecia on potato dextroxe agar at room temperature. Inoculation of healthy leaves and fruits with each fungus resulted in development of symptoms of leaf blotch and stem-end rot similar to those observed in the field. G. comari and Z. fragariae were reisolated from newly developing lesions on symptomatic leaves and fruits. Since 1996, stem-end rot has been observed more frequently in fruit production areas in the central coast of California, particularly during wet years.
Reference: (1) A. Bolay. Ber. Schweiz. Bot. Ges. 81:398, 1971. (2) J. Fall. Can. J. Bot. 32:172, 1954.
