Apparent induction of mutants and enhancement of conidial formation by fungicides in Alternaria mali

Of approximately 120.000 homokaryotic conidia ofAlternaria mali exposed to 6 fungicides, 22 variants were induced. Six were induced by zineb, 5 by maneb, 4 by nabam, 3 by ferbam, 2 by thiram, and 2 by captan. Colonies of the variants could be distinguished by growth rate, colony characteristics, and conidial production on 5 different media: Sabouraud's, cornmeal, potato dextrose, Czapek's and male extract agars. The homokaryotic organisms did not adapt to any of the fungicides after 10 generations. When exposed to fungicide decomposition products conidial germination was greatly reduced; conidial production, however, was greatly enhanced.