VARIATION IN THE CULTURAL CHARACTERISTICS AND PATHOGENICITY OF FUSARIUM AVENACEUM AND F. ARTHROSPORIOIDES

Abstract

Variants which occurred commonly in isolates of Fusarium avenaceum and F. arthrosporioides from diseased roots of alfalfa and other hosts in Alberta were of two kinds, viz., culture variants arising as sectors or patches in mycelial colonies of the parent wild type, and spore variants developing from single macroconidia. Both kinds appeared under a wide range of environmental and nutritional conditions, but they were distinct from the temporary, cultural changes which could sometimes be induced by varying these conditions. The culture variants were mostly mycelial and tended to revert partially to the wild type, or to produce other variants. Relatively stable, heavily sporulating types predominated among the spore variants. Variation followed a similar pattern in the two species studied, but isolates differed greatly in respect to number and type of variants produced. Some isolates which were relatively stable in culture produced many spore variants, and vice versa. Taxonomic comparisons indicated that classification should be based on the original characteristics of the wild types rather than on their range of cultural variation.The wild types remained viable longer than any of the variants in dried soil culture. Soil culture proved suitable for inoculum and storage purposes since variants developed infrequently in this medium.All variants proved less virulent than their parent wild types in infection tests on roots of alfalfa and sweet clover. These results emphasize the necessity of using the wild types of stable isolates in varietal resistance tests and other infection experiments.