Effects of hardening and plant age on development of resistance to cottony snow mold (Coprinus psychromorbidus) in winter wheat under controlled conditions

The development of resistance in winter-wheat seedlings to the cottony snow mold pathogen, Coprinus psychromorbidus Redhead et Traquair, was studied under controlled-environment conditions. Resistance was measured by the percentage of inoculated plants surviving after incubation at −3 °C for 8–12 weeks. The number of weeks of prehardening growth prior to inoculation, fresh weight, LT 50 , and tiller number were positively correlated with resistance to C. psychromorbidus. Prehardening temperatures of 7 and 15 °C favored development of snow mold resistance compared with 2 °C, but the LT 50 (50% killing temperature) values of uninoculated plants were not significantly different. After 1 and 2.5 weeks growth at 20 °C, plants hardened at 2 °C and 12-h day length gradually increased in resistance to snow mold from 1 to 15 weeks of hardening. Development of resistance to C. psychromorbidus in winter wheat was most influenced by the amount of prehardening growth, and the development of freezing resistance played a minor role in disease resistance development. This form of resistance, which develops with increasing plant age, appeared to reduce the rate of infection and disease development by C. psychromorbidus.