Low-temperature stress has become an important abiotic factor affecting high and stable wheat production. Therefore, it is necessary to take appropriate measures to enhance low-temperature tolerance in wheat. A pot experiment was carried out using Yannong19 (YN19, a cold-tolerant cultivar) and Xinmai26 (XM26, a cold-sensitive cultivar). We employed traditional phosphorus application (TPA, i.e., R1) and optimized phosphorus application (OPA, i.e., R2) methods. Plants undertook chilling (T1 at 4 °C) and freezing treatment (T2 at −4 °C) as well as ambient temperature (CK at 11 °C) during the anther differentiation period to investigate the effects of OPA and TPA on photosynthetic parameters and the accumulation and distribution of dry matter. The net photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate (Tr) of flag leaves decreased in low-temperature treatments, whereas intercellular carbon dioxide concentration (Ci) increased. Compared with R1CK, Pn in R1T1 and R1T2 treatments was reduced by 26.8% and 42.2% in YN19 and 34.2% and 54.7% in XM26, respectively. In contrast, it increased by 6.5%, 8.9% and 12.7% in YN19 and 7.7%, 15.6% and 22.6% in XM26 for R2CK, R2T1 and R2T2 treatments, respectively, under OPA compared with TPA at the same temperature treatments. Moreover, low-temperature stress reduced dry matter accumulation at the reproductive growth stage. OPA increased dry matter accumulation of vegetative organs after the flowering stage and promoted the transportation of assimilates to grains. Hence, the grain number per spike (GNPS), 1000-grain weight (TGW) and yield per plant (YPP) increased. The low-temperature treatments of T1 and T2 caused yield losses of 24.1~64.1%, and the yield increased by 8.6~20.5% under OPA treatments among the two wheat cultivars. In brief, OPA enhances low-temperature tolerance in wheat, effectively improves wheat architecture and photosynthesis, increases GNPS and TGW and ultimately lessens yield losses.

Due to global warming, late-spring coldness affecting wheat (LSCW) is one of the major abiotic adversities affecting wheat production. A combination of field and pot trials were conducted in this study. In the field experiment, 20 wheat varieties from the main wheat-producing areas in China were selected as experimental materials. By exploring the effects of LSCW on the spikelet characteristics and yields of different varieties, the evaluation methods and indexes of wheat varieties’ resistance to LSCW were established. Three varieties with strong resistance to LSCW (Yannong19, Guomai9, and Shannong17) and five varieties sensitive to LSCW (Zhengmai895, Xinmai26, Zhengmai366, Zhengmai8329, and Fanmai5) were screened out. The wheat varieties Yannong19 (YN19), with a strong resistance to LSCW, and Xinmai26 (XM26), with LSCW sensitivity, were selected as the test materials for the pot experiment. The ultrastructure changes in the wheat in different low-temperature treatments during the anther differentiation period were observed using an ultra-low-temperature artificial climate incubator set to 4 °C and −4 °C for 4 h (1:00–5:00 a.m.). The average temperature of the field during the low-temperature treatment was 10 °C, which was the control temperature (CK). The results showed that the cell morphology and chloroplast and mitochondrial structures of the functional leaves, young ears, and internodes below the ears were damaged, and the degree of damage was related to the cell location, the extent of low-temperature stress, and the resistance of the varieties. The degree of damage to the wheat cells was found to occur in the following order: young ears > internode belove young ears > functional leaves. The degrees of damage to the wheat cell, chloroplast, and mitochondrial structures increased with the intensification of the low-temperature stress. The damage to the XM26 variety was obviously greater than that inflicted on the YN19 variety. The anatomical mechanism of YN19 cells makes the cell structure more stable during late-spring coldness.