Isolation and Pathogenicity ofPhytophthora cactorumfrom Forest and Ginseng Garden Soils in Wisconsin

Experiments were conducted to determine if Phytophtora cactorum is present in forest soils in ginseng (Panax quinquefolius) growing areas of Wisconsin and to determine whether the isolates recovered are pathogenic to American ginseng. An apple cotyledon bioassay was used to bait P. cactorum from three of 10 forest soils and three of 10 ginseng garden soils. Twenty-two isolates from infected cotyledons were tested for pathogenicity on 3-wk old ginseng seedlings. All 10 isolates of P. cactorum from ginseng garden soils were pathogenic to ginseng, but only one of 12 forest soil isolates was pathogenic, and it was weakly virulent. The remaining 11 forest soil isolates failed to cause disease (...)