PATHOLOGICAL AND PHYSIOLOGICAL CHARACTERI ZATION OF 2 VERTICILLIUM-ALBO-ATRUM POPULATIONS ISOLATED FROM ALFALFA AND POTATO

Pathogenicity and growth of strains of Verticillium albo-atrum recover ed from alfalfa (Medicago sativa) and potato (Solanum tuberosum) were determined. On alfalfa, the alfalfa strains were more virulent than th e potato strains, and only the potato strains were virulent on potato. The optimum temperature for growth was 20 degrees C for potato strain s, and 20-25 degrees C for alfalfa strains on potato dextrose agar. At 30 degrees C, no alfalfa strain was killed whereas this temperature w as lethal for 75% of the potato strains. On Fries medium, the potato s trains produced three to four times more dry weight than the alfalfa s trains. However, on a solid medium amended with potassium chlorate, a significant inhibition was noted for potato strains as compared to alf alfa strains. These results indicate that V. albo-atrum strains isolat ed from alfalfa and potato form two pathologically and physiologically distinct groups.