Effect of potassium foliage application post-anthesis on grain filling of wheat under drought stress

Potassium foliage application of (KFA) is widely used for wheat production in China. The objective of this study was to investigate the effect of KFA on grain filling of wheat under different soil moisture conditions and the underlying mechanisms. The results indicate that KFA increased the zeatin (Z), Z riboside (ZR), and abscisic acid (ABA) contents and the ethylene (ETH) evolution rate in inferior grains during the early and middle grain filling stages, which promoted sink strength. However, KFA decreased the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), as well as the soil-plant analyses development (SPDA) value and increased the malondialdehyde (MDA) content in the flag leaves. The effect of KFA on grain filling also exhibited a notable genotypic difference. In the heavy-panicle cultivar, KFA had no significant effect on grain filling under the well-watered (WW) treatment, but it decreased the rate and active period of the grain filling of inferior grains and significantly decreased the grain weight following soil-dried (SD) treatment. In the light-panicle cultivar, KFA significantly promoted the grain filling rates of inferior grains and increased the grain weight under the WW treatment. However, KFA significantly decreased the active grain filling period but increased the grain filling rate and, therefore, had no significant effect on the grain weight under the SD treatment.