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Glycosidase Activity and Flavonoid Accumulation in Alfalfa Infected by Ascochyta imperfecta. Arthur F. Olah, Graduate Assistant, Department of Plant Pathology, North Carolina State University, Raleigh 27607, Present address of senior author: Department of Biology, Frostburg State College, Frostburg, Maryland 21532; Robert T. Sherwood, Plant Pathologist, Crops Research Division, ARS, USDA, Present address: U. S. Regional Pasture Research Laboratory, University Park, Pennsylvania 16802. Phytopathology 63:739-742. Accepted for publication 20 December 1972. DOI: 10.1094/Phyto-63-739.

When Medicago sativa leaves were inoculated with Ascochyta imperfecta β-glucosidase activity increased steadily, beginning 2 days after inoculation. This increase was paralleled by the appearance and accumulation of the aglycones of certain flavonoid glycosides which are constituents of healthy alfalfa leaves. Flavonoid glycosides isolated from healthy plants were hydrolysed by glycosidase preparations from healthy leaves, infected leaves, or cultures of A. imperfecta. The pH optimum of β-glucosidase from healthy leaves was 6.5, whereas that from diseased leaves or from pure cultures of A. imperfecta was 5.0 to 5.5. In disk-gel electrophoresis, β-glucosidase enzyme bands from diseased leaves corresponded to those from A. imperfecta. It is suggested that glycosidases, possibly of fungal origin, may partly account for pathogen-induced accumulation of flavonoid aglycones in alfalfa.