A Fusarium wilt of Tagetes marigolds

Olsen, C.M.

Phytopathology 55(7): 711-714


ISSN/ISBN: 0031-949X
Accession: 014306770

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A vascular wilt caused heavy losses of African marigold (Tagetes erecta) in southern California seed fields in the fall of 1957. Pathogenicity of the Fusarium oxysporum consistently isolated from these plants was shown with single-spore cultures in steamed soil. A 97-100% loss occurred in the original field variety, but many other commercial varieties were resistant. Mycelium extended to within a few cm of the plant apex, and seed transmission (2-10%) occurred. Most commercial varieties of China aster (Callistephus chinesis) were highly susceptible to the aster and Tagetes forms, ex-pressing similar symptoms. Tagetes erecta was highly susceptible to the Tagetes Fusarium but less susceptible to the aster form. A reselec-tion of Ball White aster, of which 73.4% of the plants were resistant to aster wilt, and the French marigold (T. patula) were highly resistant to the Tagetes forms. Other composites such as Dahlia, Chrysanthemum (Shasta daisy), Bellis (English daisy), Calendula, Dimorphotheca, Gaillardia, and Zinnia were immune. About 45% of the plants of Centaurea Double Blue Boy were susceptible. Pathogenicity to Tagetes was retained following passage through aster or Centaurea, or growth in culture for at least 1.5 years. Cultures of the aster-wilt and Tagetes-wilt organisms are morphologically similar. Evidence is presented that these races are the same forma specialis of F. oxysporum. The aster-wilt race is designated as race 1 and the Tagetes isolate as race 2 of F. oxysporum f. callistephi.