First and fourth authors: Department of Biology, University of Waterloo, Waterloo, Ontario, N2L 3G1, Canada; and second and third authors: Department of Environmental Biology, University of Guelph, Guelph, Ontario, N1G 2W1, Canada
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Accepted for publication 15 December 1999.
We examined the ability of snow molds to grow at temperatures from -5 to 30°C and to influence the growth of ice through assays for ice nucleation and antifreeze activities. Isolates of Coprinus psychromorbidus (low temperature basidiomycete variant), Microdochium nivale, Typhula phacorrhiza, T. ishikariensis, T. incarnata, and T. canadensis all grew at -5°C, whereas Sclerotinia borealis and S. homoeocarpa did not grow at temperatures below 4°C. The highest threshold ice nucleation temperature was -7°C. Because snow molds are most damaging to their hosts at temperatures above this, our results imply that the pathogenesis of these fungi is not dependent on ice nucleation activity to cause freeze-wounding of host plants. All snow molds that grew at subzero temperatures also exhibited antifreeze activity in the growth medium and in the soluble and insoluble hyphal fractions, with the exception of M. nivale and one isolate of T. canadensis. The lack of high ice nucleation activity combined with the presence of antifreeze activity in all fungal fractions indicates that snow molds can moderate their environment to inhibit or modify intra- and extracellular ice formation, which helps explain their ability to grow at subzero temperatures under snow cover.
© 2000 The American Phytopathological Society