Pathogenicity of Phoma medicaginis var. medicaginis to Roots of Alfalfa. R. Rodriguez, Department of Plant Pathology, The Pennsylvania State University, USDA Regional Pasture Research Laboratory, University Park, PA 16802. K. T. Leath and R. R. Hill, Jr. USDA, Regional Pasture Research Laboratory, University Park, PA 16802. Plant Dis. 74:680-683. Accepted for publication 21 February 1990. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/PD-74-0680.

The pathogenicity of Phoma medicaginis var. medicaginis on roots of alfalfa (Medicago sativa) was investigated in greenhouse and growth chamber experiments. Conidia were applied to roots of 4- to 6-mo-old plants grown in agar, nutrient solution, or greenhouse potting mix. All inoculations caused necrosis of main and lateral roots. P. m. var. medicaginis, in the absence of other organisms, penetrated intact roots and caused a black, dry necrosis. Wounding increased the extent and frequency of necrosis, and disease from root inoculations reduced stem number, crown diameter, and dry weight of roots and foliage of greenhouse-grown plants. P. m. var. medicaginis should be considered a primary pathogen of alfalfa roots.

Keyword(s): root rot complex.