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First Report of Brown Rot in Wine Grapes Caused by Monilinia fructicola in Canada

A survey was conducted in 2001 and 2002 to determine incidence of fruit pathogens in wine grapes (Vitis vinifera), an important crop in the southern interior of British Columbia (BC), Canada. Grape clusters were sampled every 2 weeks from June to October at eight vineyard sites located from Osoyoos in the south to Kelowna, approximately 100 km to the north. In the laboratory, the berry clusters were surface disinfested for 0.5 min in 70% ethanol, followed by 1 min in 0.5% sodium hypochlorite, and rinsed twice in sterile distilled water. The berries were placed on potato dextrose agar (PDA) amended with 15 ml/liter of 85% lactic acid and incubated at 20°C for 1 week. During the 2002 survey, a fungus resembling Monilinia fructicola (G. Wint.) Honey was observed sporulating on immature ‘Pinot noir’ grapes from Kelowna that were sampled on 14 August. Later in the growing season, a similar fungus was detected on ‘Riesling’ grapes from Summerland sampled on 11 September. There was no evidence of brown rot near the vineyard in Kelowna, but diseased stonefruit were present near the vineyard in Summerland. Subsequent identification of the fungus from ‘Riesling’ as M. fructicola was based on morphological characters and DNA sequence data for the internal transcribed spacer (ITS) regions of the nuclear ribosomal rRNA genes. The sequenced isolate was deposited in the Canadian Collection of Fungus Cultures as DAOM 231119, and the ITS sequence was accessioned in GenBank as AY289185. Colony growth on PDA was rapid and in concentric rings with the colony margin complete, microconidia abundant, and macroconidia 12 to 13 μm long. Macroconidia germinated with a long germ tube before branching. These characteristics distinguished this fungus from M. laxa, a closely related species that is slow growing with lobed colony margins, produces few microconidia, and germ tubes that branch close to the conidium (1). The complete ITS sequence for DAOM 231119 was a 100% match to other sequences deposited for M. fructicola (Z73777, AF010500, and U21815). On the basis of comparisons of available data, ITS sequences for M. fructicola (three complete ITS, seven partial ITS) and M. laxa (8 complete ITS, 10 partial ITS) differed consistently at four nucleotide positions. The fungus identified as M. fructicola was tested for pathogenicity on mature surface-sterilized ‘Pinot noir’ and ‘Riesling’ grapes. Under humid conditions, buff-colored sporodochia bearing conidia developed over the surface of the infected berries. This indicates that M. fructicola can cause decay of wine grapes and could be confused with bunch rot caused by Botrytis cinerea. Previously, M. fructicola was reported on grapes in Oklahoma, but likely these grapes were not Vitis vinifera (2). To our knowledge, this is the first report of brown rot caused by M. fructicola on wine grapes in North America.

References: (1) L. R. Batra. World Species of Monilinia (Fungi): Their Ecology, Biosystematics and Control. Mycologia Memoir No. 16. Gerbrüder Borntraeger, Berlin/Stuttgart, 1991. (2) D. A. Preston. Host Index of Oklahoma Plant Diseases, Tech. Bull. No. 21. Oklahoma Agricultural and Mechanical College, Agricultural Experiment Station, Stillwater, 1945.