First report of anthracnose caused by Elsinoe ampelina on grapes in Michigan

In 2001, dark brown-to-purple, sunken lesions were observed on shoots and berries of 5-year-old 'Mars' and 'Marquis' table grapes (Vitis spp.) in Onondaga, MI. The disease affected >90% of the vines. Many leaves were curled and distorted and some shoot tips had died back. Older wood showed crater-like indentations. No fruit was harvested due to poor fruit quality. Lesions (at least 10 per sample) were surface-disinfested with 1% sodium hypochlorite, placed on potato dextrose agar (PDA), and kept at 23 to 25°C under ambient light. Sphaceloma ampelinum de Bary (teleomorph Elsinoë ampelina Shear) was isolated from shoots, leaves, and clusters (4). Colonies appeared as slow-growing, dark red mounds. Conidia were hyaline, ovoid, and measured 2.5 to 5 x 5 to 12.5 μm (average 3.5 x 7.4 μm). While grape anthracnose is usually considered a southern disease, occasional outbreaks have been reported in Ohio (1) and it appears to have become more common in Michigan in recent years. Several old herbarium specimens and records of the fungus on grapes in Michigan exist (2,3), but pathogenicity was not proven. In 2004, the disease was confirmed in eight table grape vineyards (three 'Marquis', two 'Concord Seedless', two 'Mars', and one unknown variety), one juice grape ('Niagara'), and one wine grape vineyard ('Vidal') in various locations in Michigan. To determine pathogenicity, shoots of two potted 'Mars' plants were sprayed until runoff with a suspension of 10(6) conidia/ml of an isolate from 'Marquis' grapes in Lawton, MI. The plants were covered with clear plastic bags for 48 h and kept at 23 to 25°C on the lab bench for 2 weeks. Shoots sprayed with water served as controls. After 4 days, numerous brown spots appeared on inoculated young leaves, petioles, internodes, and tendrils. Lesions continued to enlarge and coalesce into large necrotic areas. The fungus was successfully reisolated on PDA using the procedure described above. ITS1F/ITS4 amplification of three isolates from 'Marquis' vineyards in St. Joseph, Lawton, and Onondaga, MI produced a product of approximately 1,040 bp. The sequences most closely matched that of E. banksiae I. Pascoe & P. Crous from Banksia prionotes Lindl. in GenBank, but no E. ampelina sequences were available for comparison. The sequences of the three isolates in this study were submitted to GenBank (Accession Nos. AY826762, AY826763, and AY826764). The disease in the vineyard in Onondaga may have been present on the plants which originated in Arkansas. Additional evidence for nursery stock as a source of inoculum was the discovery of anthracnose on 'Concord Seedless' plants at a retailer in Okemos, MI in 2004. Anthracnose was also found on riverbank grape (Vitis riparia Michx.) in Holland, MI, indicating the potential of wild hosts to be an inoculum source. However, nothing is known about the ability of isolates from wild grapes to infect cultivated grapes. Control methods, such as the use of disease-free plants, pruning, and effective fungicides are necessary to avoid serious losses in susceptible varieties, particularly in years with heavy rainfall.