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 degrees C during this treatment period had no effect on aboveground biomass, bur 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 degrees 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 degrees C lover 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. (C) 1998 Annals of Botany Company.