ROOT ROT OF GINSENG IN ONTARIO CAUSED BY MEMBERS OF THE GENUS RAMULARIA

Abstract

Two destructive diseases of the root of ginseng, Panax quinquefolium L., have assumed economic importance in the ginseng-growing districts of Ontario. The more destructive of the two diseases, commonly known as the disappearing-rot, is characterized by the fact that affected roots may, in a relatively short time, either completely disappear in the soil or leave as evidence of their presence only a peridermal shell enclosing fragments of vascular tissue. The disease, which is non-systemic, is caused by at least three representatives of the genus Ramularia of the Fungi Imperfecti, one of which has been identified as Ramularia panacicola Zins., and the other two being new to science, are described as new species for which are proposed the binomials, Ramularia mors-panacis and Ramularia robusta. No sexual stage has been observed in connection with the three species. They appear to persist in the soil indefinitely either saprophytically or in a dormant condition.The name rust has been applied to the other serious but less destructive disease because of the occurrence on the surface of affected roots of superficial, rust-colored lesions. The cause of the rust disease has not been definitely established but the evidence thus far suggests that it is probably also caused by representatives of the genus Ramularia.Rotation and rigid sanitation are the only control measures suggested, resistant varieties not having been encountered.In the present work a large number of additional representatives of the genus, different from each other and from the isolants from ginseng, have been obtained from tissue isolations from similar lesions on various other hosts. Cross-inoculations indicate variations in pathogenicity among the isolants and specificity in host relations. This demonstration of the universal occurrence and parasitic capabilities of soil-inhabiting representatives of the genus Ramularia changes the concept of the genus and adds a most important member to the group of facultative parasites associated with root troubles of plants.