Disease Note.

First Report of Powdery Mildew on Ginseng in North America. P. L. Sholberg, Agriculture and Agri-Food Canada, Summerland, British Columbia VOH IZ0; T. Li, Agriculture and Agri-Food Canada, Summerland, British Columbia VOH IZ0; and J. Ginns, Agriculture and Agri-Food Canada, Centre for Land and Biological Resources Research, Ottawa, Ontario K1A 0C6. Plant Dis. 80:463. Accepted for publication 15 February 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-0463C.

In the summer of 1995 a powdery mildew was observed on American ginseng (Panax quinquefolium L.) plants at the Agriculture and Agri-Food Canada Research Centre, Summerland, British Columbia. The disease was found in a 20 x 30 m ginseng research plot where 3-year-old plants were growing on raised beds and under artificial shades (78% light reduction). The upper surface of five to 10 leaflets on many of the plants was covered with colonies of extensive, white, superficial mycelium. These leaves became yellow and fell prematurely. No infections of berries or stems were observed. The fungus produced abundant cylindrical to oblong arthroconidia that were about 40 x 14 µm and were borne singly on simple conidiophores 60 to 110 µm long and 8.0 to 8.5 µm in diameter. Yellow to brown, spherical cleistothecia-like ascocarps were found in groups of 5 to 20 on heavily infected leaves in September but few were mature. The fungus is a species of Erysiphe because there were two or more asci in each ascocarp and the appendages were hyphoid. The number of ascospores in each ascus is uncertain because few mature asci were seen but seven elliptical immature ascospores (approximately 22 x 13 µm) were observed in each ascus. A powdery mildew was reported in China on both Asian and American ginseng (1), and was referred to as Erysiphe panax Bai & Wang. However, efforts to obtain the original description of E. panax, in order lo compare that species with this fungus, have been unsuccessful. Although a name cannot be applied to our specimen at present,, this is the first report of a powdery mildew on ginseng in North America. This disease could seriously reduce seed production, root fresh weight, and winter hardiness of ginseng plants. A voucher specimen has been deposited in the National Mycological Herbarium of Canada under accession number 221951