Rate of Development of Postanthesis Water Deficits and Grain Filling of Spring Wheat

Wheat crops ( Triticum aestivum L.) often experience water deficits during grain filling, thereby reducing grain yield. We determined the effect of the rate of development of postanthesis water deficits on the grain growth of wheat. Plants were grown in a pot experiment in two temperature‐regulated glasshouses with similar temperatures, but with high and low relative humidities. Differences in the rate of increasing plant water deficits between the high and low humidity treatment became evident within 6 d after watering was stopped. During the first 19 d after anthesis, the rates were 0.10 and 0.18 MPa d −1 , respectively. Grain yield at low humidity was reduced by 33%, relative to high humidity, mainly as a result of a reduction in grain size. An early cessation of grain growth after mid grain filling probably induced the reduction in grain size. We conclude that differences in grain growth in the two humidity treatments resulted from the different rates of development of water deficits in the two treatments. In the low‐humidity treatment, the size of the grain in the tillers was reduced more than the size of the grain on the mainstem. The increase in the grain dry matter of the mainstem was higher than the total increase in mainstem dry matter during the grain‐filling period. The increase in grain dry matter of Tiller 1 was also higher, but in Tiller 2 it was lower, indicating that grain growth on the mainstem was probably supported by assimilates stored in the stems, leaves, and roots and by transfer of assimilates from tillers.