Contribution of the hardening period to developping freezing resistance indurum wheat (Triticum durum Desf.)

In the present study, changes in freezing resistance during the hardening o f nine durum wheat (Triticum durum Desf.) cultivars were evaluated in a phy totron in Martonvasar. Hardening was carried out at a constant temperature of +2 degrees C for 0, 10, 20, 30, 40, 50, 60, 70, 80, 90 or 100 days, afte r which the plants from all the treatments were frozen at -13.5 degrees C. Considerable varietal differences in the hardening kinetics were recorded f or the durum genotypes investigated. The freezing resistance of the genotyp es was negligible after 0-20 days of hardening. The maximum degree of freez ing resistance was reached after 30-50 days of hardening. A considerable de crease in freezing resistance was observed in plants kept at +2 degrees C f or 60 days or more. Judging by the results of these and earlier experiments , on average T. durum genotypes achieve a lower level of hardening, which g enerally has a shorter duration, than that observed in winter T, aestivum c ultivars.