Effect of High Temperature Stress at Anthesis on Grain Yield and Biomass of Field-grown Crops of Wheat

Spring wheat ( Triticum aestivum L., ‘Chablis’) was grown under field conditions from sowing until harvest maturity, except for a 12-d period [70–82 days after sowing (DAS) coinciding with anthesis] during which replicated crop areas were exposed to a range of temperatures within two pairs of polyethylene-covered temperature gradient tunnels. At 82 DAS, an increase in mean temperature from 16 to 25 °C during this treatment period had no effect on above-ground biomass, but increased ear dry weight from 223 to 327 g m -2 and, at 83 DAS, reduced root biomass from 141 to 63 g m -2 . Mean temperature over the treatment period had no effect on either above-ground biomass or grain yield at maturity. However, the number of grains per ear at maturity declined with increasing maximum temperature recorded over the mid-anthesis period (76–79 DAS) and, more significantly, with maximum temperature 1 d after 50% anthesis (78 DAS). Grain yield and harvest index also declined sharply with maximum temperature at 78 DAS. Grain yield declined by 350 g m -2 at harvest maturity with a 10 °C increase in maximum temperature at 78 DAS and was related to a 40% reduction in the number of grains per ear. Grain yield was also negatively related to thermal time accumulated above a base temperature of 31 °C (over 8 d of the treatment from 5 d before to 2 d after 50% anthesis). Thus, grain fertilization and grain set was most sensitive to the maximum temperature at mid-anthesis. These results confirm that wheat yields would be reduced considerably if, as modellers suggest, high temperature extremes become more frequent as a result of increased variability in temperature associated with climate change. Copyright 1998 Annals of Botany Company