VIEW ARTICLE

Effect of Disease and Injury on Accumulation of a Flavonoid Estrogen, Coumestrol, in Alfalfa. R. T. Sherwood, Crops Research Division, ARS, USDA, and Departments of Plant Pathology, Animal Science, and Biochemistry, North Carolina State University, Raleigh 27607; A. F. Olah(2), W. H. Oleson(3), and E. E. Jones(4). (2)(3)(4)Crops Research Division, ARS, USDA, and Departments of Plant Pathology, Animal Science, and Biochemistry, North Carolina State University, Raleigh 27607. Phytopathology 60:684-688. Accepted for publication 10 November 1969. DOI: 10.1094/Phyto-60-684.

Coumestrol accumulated in alfalfa in response to infection by all the pathogenic fungi tested: Ascochyta imperfecta; Cylindrocladium scoparium; Colletotrichum trifolii; and Uromyces striatus. The time course of accumulation paralleled the development of infection, and the concentration of coumestrol was related to the degree of infection. Final steps of coumestrol synthesis occurred only in the infected parts of the plant. Coumestrol was not translocated from the infected areas to other parts of the plant. Very little coumestrol accumulated in leaves inoculated with nonpathogenic fungi or with a pathogenic bacterium, Xanthomonas alfalfae, but coumestrol did accumulate when nonpathogenic fungi were incubated on detached leaves. Coumestrol did not accumulate in plants inoculated with the alfalfa mosaic virus or the stem nematode (Ditylenchus dipsaci) or in leaves injured by mechanical means, atmospheric oxidants, or desiccation. Treatment with a Cu++ solution resulted in accumulation of coumestrol in roots, but not in shoots. Ascochyta imperfecta did not synthesize coumestrol when it was grown on media prepared from alfalfa. Hypotheses concerning the nature of pathogen-induced flavonoid biosynthesis and its relation to phytoalexin production are presented.