Vernalization studies with Pacific Northwest wheat

Lack of rain or excess soil moisture may create problems for fall sowing of winter cereals in the Pacific Northwest. Growers unable to plant in the fall question the potential for late winter sowings, which is determined to a large extent by cultivar vernalization requirement. This study was conducted to gain a better understanding of the vernalization requirement of winter wheat (Triticum aestivum L.) cultivars grown in the region and to determine if a tool could be developed for predicting latest winter sowing dates. A growth chamber-greenhouse procedure was developed to determine the relative vernalization requirement of new wheat cultivars. Twenty cultivars were sown in the field at intervals from early October through late March during the 1991-1993 cropping seasons. Accumulated heat units from sowing were used to determine vernalization days (VD). Heading date and yield were measured. Field results indicated that cultivars could be categorized in three groups-those with low, intermediate, and high vernalization requirements. Growth chamber-greenhouse results verified these groupings. Field data suggest that if 50% relative yield (late-sown yield is 50% of that for the same cultivar when sown in fall or early winter) is acceptable, then cultivars with a low vernalization requirement can be sown with 60 VD expected after sowing while cultivars with a high vernalization requirement require 70 expected VD. If 70% relative yield is desired, all cultivars tested showed similar performance.