Yield and Development of Winter Wheat at Elevated Temperatures

The influence of temperature on wheat (Triticum aestivum L.) yield components is known to differ depending on plant growth stage. Our objective was to determine how increased temperatures at five growth stages influenced development, yield, and yield components of winter wheat. Field experiments were conducted on the semi-dwarf cultivar Newton grown in Eudora silt loam (coarse-silty, mixed, mesic Fluventic Hapludolls). Transparent plexiglass chambers occupying 1.1 m² of crop surface were heated continuously an average of 3.4 and 6.4°C above ambient temperatures during double ridge, terminal spikelet, stem extension, anthesis, and milky ripe developmental stages. Because the rate of development depends primarily on temperature, the treatments were expressed as accumulated thermal units (TU = Σ max °C + min °C/2) above ambient TU during each growth stage; where TU is thermal units, and max °C and min °C are maximum and minimum daily temperatures, respectively. At harvest, plot yields were determined and yield components estimated. Compared with controls, kernel weights were significantly increased by temperature treatments of 48 TU at double ridge in 1978-1979 (P ≤ 0.05) and 44 TU in 1979-1980 (P ≤ 0.10). High temperature treatments at terminal spikelet in 1978-1979 reduced kernels per head (P ≤ 0.5) from 19.1 to 15.4, at least partly by reducing grain-bearing spikelets per head. An increase in kernel weight was associated with that reduction in kernels per head so final yield was not significantly reduced. An average reduction of 2.4 kernels per head by the 101 TU treatment at anthesis significantly reduced yield in 1979-1980. At milky ripe, average kernel weights were generally reduced by high temperatures both years. Increasing temperatures at any of the five growth stages advanced plant development relative to control plants. Using data from both years, kernel weights correlated positively with days (r = 0.83) and accumulated TU (r = 0.84) during grain filling. Development appeared to increase exponentially when daily TU was above about 27. Advancing anthesis a few days, when subsequent temperatures are less likely to be high, may benefit kernels per head and/or average kernel weight.