Susceptibility of Grapevine Pruning Wounds and Symptom Development in Response to Infection by Phaeoacremonium aleophilum and Phaeomoniella chlamydospora.

Fresh to 10-month-old pruning wounds on grapevine cvs. Thompson Seedless and Cabernet Sauvignon were inoculated with Phaeoacremonium aleophilum or Phaeomoniella chlamydospora at approximately 1 × 106 spores/ml. Successful infection was determined by isolation of the pathogen from necrotic margins of cankers or from vascular discoloration assessed 4 months after each inoculation date. Disease incidence decreased as the length of time between pruning and inoculation increased; however, wounds remained susceptible for up to 4 months. Vascular discoloration was significantly less extensive in the noninoculated control than in inoculated spurs. Reduction of shoot length in both cultivars varied depending on pruning wound age at the time of inoculation. In a separate study, inoculation of fresh pruning wounds of Cabernet Sauvignon resulted in successful infection regardless of the time of pruning from February to December.

First Report of Blossom Blight of Strawberry Caused by Xanthomonas fragariae and Cladosporium cladosporioides in California.

In the spring of 1996, severe blossom blight occurred in some strawberry fruit production fields in the Watsonville area. The symptoms, in addition to blighting of entire flowers, were as follows: on the lower surface of the calyx, watersoaked lesions that appeared dark green under reflected light and translucent under transmitted light; necrotic calyces of seemingly healthy green and ripe fruits; watersoaking of the base of the calyx that extended into the pedicel; green-gray sporulation on dead anthers; and presence of flower clusters with small and irregularly shaped fruits. Yellow bacterial colonies were consistently isolated from water-soaked and necrotic lesions on calyces and pedicels. These colonies were entire, circular, raised, glistening, mucoid, and slow growing, characteristics typical of Xanthomonas fragariae on nutrient agar-glucose-yeast extract medium. The bacterial isolate was also identified by rep-polymerase chain reaction as X. fragariae. In addition to the yellow bacteria, a fungus was also frequently isolated from infected anthers, sepals, petals, and pistils, and was identified as Cladosporium cladosporioides. On potato dextrose agar, the fungus had velvetlike colonies colored olivaceous-green to olivaceous-brown, apically and laterally branched conidiophores, and lemon-shaped conidia that were usually smooth but sometimes textured. Blossoms of greenhouse-grown strawberry plants cv. Selva were inoculated with either or both organisms. Blossoms inoculated with X. fragariae developed symptoms distinct from those inoculated with C. cladosporioides. The most prominent visible symptoms caused by X. fragariae were watersoaked lesions on calyces that later became necrotic, watersoaking of the calyx that extended into the pedicel, and blighting of flowers and developing fruits as a result of girdling of the pedicel. Infection by C. cladosporioides was characterized by necrosis of flower parts or the entire flower, presence of green-gray sporulation on dead anthers, and production of small and malformed or misshapen fruits. Inoculation with both organisms produced all the symptoms described above in different flowers of a plant. Infection with both organisms aggravated disease severity, but each organism was capable of inducing blossom blight independently. Both organisms were reisolated from artificially inoculated strawberry flowers, fulfilling Koch's postulate for proof of pathogenicity. This is the first report of the two organisms causing blossom blight of strawberry in California. This is also the first report that C. cladosporioides is a pathogen of strawberry.

Occurrence of Leaf Blotch and Stem-End Rot of Strawberry in the Central Coast of California.

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.