Effect of freezing resistance and low-temperature stress on development of cottony snow mold (Coprinus psychromorbidus) in winter wheat

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Abstract
The relationship between snow mold resistance and freezing resistance was studied under controlled-environment conditions, using winter wheat (Triticum aestivum L. em. Thell) cultivars varying in freezing resistance and resistance to cottony snow mold (Coprinus psychromorbidus Redhead & Traquair). Cultivars varying in freezing resistance were equally susceptible to C. psychromorbidus. There existed a negative relationship between snow mold resistance and freezing resistance. Sublethal, subzero freezing temperatures between −3 and −12 °C predisposed the winter wheat cultivar 'Winalta' to increased damage by C. psychromorbidus. A synergistic effect resulting in increased mortality was observed when winter wheat plants received a combination of low-temperature stress and inoculation with C. psychromorbidus. In hardened winter wheat plants, sublethal levels of snow mold damage following 6 weeks incubation with C. psychromorbidus resulted in a reduction in freezing resistance or LT50 (50% killing temperature) of approximately 7 °C compared with the noninoculated controls. The possible role of low-temperature stress on the susceptibility of winter wheats to C. psychromorbidus and of snow mold infection on the retention of freezing resistance in winter wheats during winter in the central and northern Canadian prairies is discussed.