First report of Phomopsis viticola causing bunch rot of grapes in Australia

From 2004 to 2006, grapevines (Vitis vinifera cv. Cabernet Sauvignon) in a commercial vineyard in the Hastings Valley (north eastern Australia) were surveyed for bunch rot diseases at dormancy, flowering, berries pea-sized, veraison and harvest. During the growing season black lesions were observed on green shoots and leaves. At harvest, abundant black pycnidia were consistently observed on the surface of bunches with berries becoming desiccated and rachis necrotic (Fig. 1).

Buds, canes, leaves, flowers and bunches were surface sterilized in 1% sodium hypochlorite for 1 min, followed by three successive washings in sterile distilled water. Isolations were initially made on Dichloran Rose Bengal Chloramphenicol agar and incubated at 25°C for 7 days. Any resulting fungal growth was sub-cultured onto potato dextrose agar. The plates were incubated at 25^°C for 7 days. Phomopsis viticola was isolated from canes, leaves, flowers, rachis and bunches and identified based on morphological characteristics of the conidia. Koch’s postulates were satisfied by inoculation of Cabernet Sauvignon berries from excised bunches taken at harvest. Whole bunches were surface sterilized by dipping in 1% sodium hypochlorite for 2 min, followed by three successive washings in sterile distilled water. Berries were inoculated with a 10 µl drop of 1 × 10⁶ conidia per ml suspension. Control bunches were inoculated with 10 µl drops of sterile distilled water. Bunches were placed in plastic containers lined with sterile paper towel, moistened with sterile distilled water to maintain humidity and incubated at 23ºC for 14 days. Black pycnidia developed on the surface that eventually sporulated to produce yellow oozing of spores. Phomopsis viticola was re-isolated from the pycnidia that had formed on the berries.

Phomopsis viticola was first described as a rot of Niagara grapes in New York vineyards in 1911 by Gregory (1913), but is primarily recognised as a pathogen of the vegetative tissues. In Australia, Phomopsis viticola is a recognised pathogen of grapevine buds, canes, shoots and leaves (Merrin et al., 1995; Emmett et al., 1994). This is the first report of Phomopsis viticola causing bunch rot on grape in sub-tropical regions of Australia. Currently there are no fungicides registered for the control of Phomopsis fruit rot of grape in Australia.