Effect of phosphorus and potassium foliage application post-anthesis on grain filling and hormonal changes of wheat

Foliage application of fertilizer is an important supplement for soil application fertilizer. Phosphorus (P) and Potassium (K) are important nutrient elements that significantly affect the grain weight and grain yield of wheat, and foliage application of K and P is mainly used for wheat production in the northern dryland region of China. However, the mechanism underlying the regulation of grain filling by foliage application of K and P is not understood. In the present study, monopotassium phosphate (KH2PO4), monosodium orthophosphate (NaH2PO4) and potassium chloride (KCl) were used for foliage application at the anthesis of wheat, and the changes of IAA, ABA, Z+ZR, GAs and ETH in wheat grain were measured during the grain filling process. The objective of this study was to investigate the effect of P and K foliage application on the grain filling process of wheat and to determine how changes in the endogenous hormones of the developing grains of winter wheat under P and K foliage application are related to the grain filling process. The results indicate that the effect of P and K foliage application on the grain filling of wheat is the difference. The K foliage application significantly increased the Z+ZR and ABA contents and decreased the ETH evolution rate in inferior grains, which promoted sink strength and increased the grain filling rate and the grain weight. In comparison, the P foliage application significantly promoted the activities of SOD, POD, and CAT and decreased the MDA content in the flag leaves and relieved the premature senility of the plant, which increased the active grain-filling period and the grain weight. For the heavy panicle cultivar, foliage P had a reasonable effect on grain filling, and for the light panicle cultivar, foliage K had a reasonable effect on grain filling. The mixture of P and K had an additive effect and prevented P and K deficiencies. Foliage application of KH2PO4 is an effectual measure for promoting the grain weight of wheat.