The Relationships among the Vernalization Response, Carbohydrate Accumulation, Developmental Stages and Frost Tolerance in Bread Wheat Cultivars

Frost tolerance of winter wheat depends primarily on a strong vernalization requirement, delaying the transition to reproductive phase. The responses of four bread wheat cultivars (Triticum aestivum L.) to low-temperatures were examined in controlled environment and field conditions. Prolonged cold treatment accelerated the transition to reproductive development in winter wheats (cv. Norstar and cv. Shahryar) and facultative wheat (cv. Alvand), but not in a spring wheat (cv. Kavir). Exposure to low temperatures also enhanced frost tolerance of the winter and facultative wheats. Maximum frost tolerance was achieved around the point where further cold treatment caused no additional acceleration of flowering time; the vernalization saturation point.This greatest frost tolerance potential was observed in the winter wheat Norstar, which required the longest cold treatments to fulfill the vernalization response. The increased frost tolerance observed after exposure to low-temperatures (cold acclimation) was associated with reduced water but increased sugar content, and there was a strong association between frost tolerance and increased fructan content in the crowns. Fructan levels increased proportional to the length of cold treatment until the vernalization saturation point was reached. These data support the hypothesis that vernalization and cold acclimation pathways are interconnected in cereals and that the delay of floral development until spring is critical to allow acclimation to lowtemperatures during winter.