Grapevine (Vitis vinifera L.), cv. Red Globe, in Northern Chile was found with symptoms of shoot blight early in the spring. Symptoms consisted of elongated cankered lesions surrounded by water-soaked tissues that developed mainly at the base of new shoots. The distal part of the shoots withered. Symptoms were similar to the shoot blight caused by Botrytis cinerea Pers. early in the spring, except that superficial gray sporulation was always absent. Isolation on acidified potato dextrose agar (APDA) consistently yielded a fungus that produced white mycelium and black spherical to elongated sclerotia (2 to 10 mm in diameter); the fungus was identified as Sclerotinia sclerotiorum (Lib.) de Bary (2). New shoots were inoculated by inserting a 4-mm plug of mycelium from actively growing cultures on APDA into a cut made at the base of each of five shoots per cultivar with a sterile scalpel. Inoculated wounds were sealed with Parafilm tape to avoid rapid dehydration. Inoculated plants and an equal number of wounded but not inoculated plants of each cultivar were left as controls and maintained in a screenhouse. Inoculations of grapevine cvs. Thompson Seedless, Flame Seedless, Red Globe, Ribier, and Chardonnay with S. sclerotiorum isolates SC-1, SC-2, and SC-3 and B. cinerea (isolate BC1-3 from grapevine) resulted after 7 days of incubation in canker lesions that were similar to those observed in the field. Cankers caused by S. sclerotiorum varied significantly (P < 0.05) in length from 13.3 to 28.7 mm on ‘Red Globe’, 5.3 to 20.7 mm on ‘Thompson Seedless’, 4.0 to 17.7 mm on ‘Flame Seedless’, 2.0 to 11.3 mm on ‘Ribier’, and 0.0 to 7.6 mm on ‘Chardonnay’. Mature berries of ‘Flame Seedless’ table grapes were surface-disinfected with 1% NaOCl for 1 min, punctured with a sterile needle, and inoculated with a mycelium plug. All S. sclerotiorum isolates and the B. cinerea isolate were pathogenic on mature berries, which developed a soft rot and superficial mycelium after 5 days of incubation at 25°C in humid chambers. Reisolations from diseased shoots and rotten berries were successfully performed on APDA. We concluded that S. sclerotiorum and B. cinerea could cause canker lesions on new shoots early in the spring. S. sclerotiorum has been previously associated with soft rotting of mature berries of grapes worldwide (1), but to our knowledge, this is the first confirmed report demonstrating that S. sclerotiorum can cause shoot blight. Considering that grapevines are cultivated on 2-m-high trellises in Chile, we speculate that wind disseminated ascospores may infect shoots. However, ascocarps have not yet been found in vineyards in Chile.
References: (1) W. B. Hewitt. Berry rots and raisin molds. Pages 26--28 in: Compendium of Grape Diseases. R. C. Pearson and A. C. Goheen, eds. The American Phytopathological Society, St. Paul, MN, 1994. (2) L. Kohn. Phytopathology 69:881, 1979.