Wheat Freeze Damage Phenotypes and Associated Yield Losses.

Freeze injury is an annual concern for soft red winter wheat (SRWW) growers in North Carolina. Yield effects from individual freeze injury types are not well understood. In March 2017, temperatures at Union and Rowan County Official Variety Tests (OVT) were below freezing for 52 and 92 hours, respectively. This followed a February where average daily temperatures were above 50^oF, and SRWW growth stages were between Zadoks 28 and 45 at the time of the freeze. While damaging temperature thresholds have been well documented in hard red winter wheat across many growth stages, freezing temperature yield impacts are primarily focused on head damage in the boot stage with little reporting on impacts in other growth stages. In ten varieties across a range of maturities at both locations we marked 50 individual tillers based on a range of damaged tiller types: healthy tillers, normal primary tillers, normal secondary tillers, dead flag leaves, and tillers with stem damage. All tillers were collected at maturity and analyzed for head development, kernel number and kernel weight. Healthy tillers averaged 23.4 kernels per head, primary tillers 21.7, secondary tillers 21.8, damaged flag leaf 8.3, and stem-damaged tillers 16.9 kernels per head. The effect of damaged tiller type was significant for kernel number at p < 0.05. Percent head development followed these trends. Flag leaf damage resulted in 92% head loss across all varieties, less kernel production, and lower thousand kernel weight, compared to healthy tillers where only 33% of heads were lost. Flag leaf damage followed by damaged stems were the most devastating factors affecting yield loss following a freeze prior to boot stage in SRWW. Quantifying the effect of factors influencing yield losses can aid growers in making decisions about crop destruction or additional necessary inputs to realize a profitable yield.