Quantifying Wheat Vernalization, Photoperiod, and Freeze Tolerance In Controlled Environment Studies to Predict Survival At Variable Planting Dates.

In the Pacific Northwest (PNW) spring and winter off-season planting times of wheat could better utilize winter moisture and increase rotation options. Nine adapted PNW wheat cultivars with spring, winter, and facultative habit were evaluated in three controlled environment studies to quantify vernalization, photoperiod, and freeze tolerance in conjunction with multi-location field planting date trials. Vernalization response was assessed at six different near-freezing cold exposure intervals by scoring final main stem leaf number (FLN) at heading. Vernalization response was fitted to a nonlinear function to characterize vernalization amplitude and duration. Photoperiod was elicited by growing plants at two different day lengths in controlled chambers and scoring for FLN. Freezing response at several temperatures characterized the 50% lethal cold dose (LD₅₀) using probit analysis. Vernalization response showed a large decline in FLN as vernalization interval increased for winters, with smaller reduction in facultative, and no response by the spring cultivars. Cultivars with response showed variation in duration needed for full vernalization. All winter cultivars were photoperiod sensitive, facultative has split sensitivity, and spring cultivars were insensitive. Cold tolerance LD₅₀ varied, with the spring cultivars LD₅₀ between -6.5ºC and -8.7ºC, the facultative cultivars between -11ºC and -12.2ºC, and the winter cultivars were below -14ºC. Vernalization duration and amplitude of response correlated with field survival as well as maturity timing. Freeze tolerance tests were highly correlated with field survival trends. Photoperiod was less useful for prediction of survival, but insensitivity is desirable for off season plantings.