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Degradation of Alfalfa Phytoalexin by Stemphylium loti and Colletotrichum phomoides. Verna J. Higgins, Graduate Assistant, Department of Plant Pathology, Cornell University, Ithaca, New York 14850; R. L. Millar, Professor, Department of Plant Pathology, Cornell University, Ithaca, New York 14850. Phytopathology 60:269-271. Accepted for publication 5 September 1969. DOI: 10.1094/Phyto-60-269.

Stemphylium loti, a weak pathogen of alfalfa, induced production of phytoalexin by alfalfa, but only small amounts of the phytoalexin were detected in infection drops. The phytoalexin was rapidly degraded by S. loti in vitro; degradation proceeded concomitantly with the production of a compound (λ max 285 mµ) that inhibited germ tube growth of S. loti. Colletotrichum phomoides, a nonpathogen of alfalfa, effected slow degradation of alfalfa phytoalexin in vitro and concomitant production of a compound that inhibited germ tube growth of C. phomoides and had an ultraviolet absorption spectrum similar to that of the phytoalexin, but differing in its solubility in CCl₄.