During the summer of 2004, a root rot was observed on 3- and 4-year-old American ginseng cultivated in the Beijing area, and in 2006, the root rot was also found in the Hebei Province. The root epidermis appeared light brown with irregular lesions in the early stage. Sometimes the lesions had defined edges and were striped. In the later stages of the disease, the roots had splits in the epidermis and a rotted cortex causing them to lose commercial value. Plants wilted when the roots were severely damaged. The diseased roots were assayed for plant parasitic nematodes. A plant parasitic nematode was identified as Ditylenchus destructor on the basis of the following characteristics (1): stylet length ranged from 9.2 to 13.3 μm with rounded knobs; a single anterior outstretched ovary extended toward the base of the esophagus; the developing oocytes existed in two rows, changing to one near the middle of the ovary, and the vulva was thick and elevated, with the posterior uterus extending approximately three-quarters of the distance to the anus; the bursa extended from opposite the anterior end of the spicules approximately three-fourths of the tail length; and the tail was rounded and the lateral field had six incisures. Pathogenicity was tested by inoculating with a 2-ml suspension (approximately 2,000 nematodes) extracted from diseased roots to each of seven intact American ginseng roots. The roots were in a polyethylene bag surrounded by sterile soil and incubated at 25 ± 2°C. On five roots after 60 days, symptoms were similar to those observed in the field, and D. destructor was isolated from the infected parts. The control, inoculated only with sterile water, remained healthy. To our knowledge, this is the first report of D. destructor causing root rot of American ginseng.
Reference: (1) G. Thorne. Proc. Helminthol. Soc. Wash. 12:27, 1945.
