First Report of Fusarium oxysporum on Purple Coneflower

The narrow-leaf purple coneflower Echinacea angustifolia DC. is a perennial composite native to the central Great Plains. Because of its potential ornamental and pharmacological value, Echinacea is currently being brought into commercial production in South Dakota. A blight or wilt was observed in a field research plot on 1- to 3-year-old plants in the summers of 1993 and 1994. Affected plants showed necrosis along leaf margins, followed by wilting and eventual death. Examination of roots and stems revealed darkening of the vascular and ground tissues. Up to 5% of plants growing in the wetter portion of the field developed symptoms. No infected plants were found in the well-drained portions of the field. Plants displaying disease symptoms were also observed in cuttings and seedlings grown in the greenhouse. The pathogen was consistently isolated by plating 0.5-cm sterile stem segments on lactic acid potato dextrose agar. To complete Koch's postulates, a single hyphal tip of the pathogen was transferred to carnation leaf agar. Micro and macro conidia formed abundantly within 10 days and matched the description of Fusarium oxysporum Schlechtend.:Fr. Two- to 3-month-old coneflower seedlings, representing the full range of genetic diversity from our Echinacea collections, were inoculated with the isolated pathogen by placing six 2-mm-diameter mycelial plugs directly on the roots of each plant, just below the soil surface. Inoculated seedlings were placed in the greenhouse to allow development of the infectious agent. Infected seedlings showed typical diagnostic symptoms (30% of inoculated seedlings) within 3 weeks. Noninoculated plants remained symptomless. F. oxysporum was reisolated from the seedlings as above. This is the first report of F. oxysporum as a pathogen on E. angustifolia.