Foliar Application of TiO2 Alleviates the Adverse Effects of Late Sowing by Optimizing Photosynthetic Physiology, Yield, and Quality in Wheat.

Late-sown wheat, which misses the optimal photoperiod and temperature for growth, suffers irreversible losses in both grain number per spike and thousand-grain weight, resulting in severe yield reductions. To this end, a two-year field experiment was conducted to evaluate the effects of application timing (S1 at the booting stage and S2 at the flowering stage) and concentration (T0 = 0 μmol L-1, T1 = 376 μmol L-1, T2 = 501 μmol L-1, T3 = 626 μmol L-1) on the photosynthetic physiology, grain number per spike, thousand-grain weight, and quality of late-sown wheat, aiming to elucidate the mechanism by which TiO2 enhances the yield quality-efficiency relationship in wheat. The results showed that the foliar application of TiO2 significantly enhanced the accumulation of photosynthetic pigments (SPAD) and spectroscopic indices (CHI, PRI) in wheat flag leaves, markedly improved the net photosynthetic rate, and increased the activities of antioxidant enzymes (SOD, POD) while reducing the accumulation of membrane lipid peroxidation products (MDA), with the T2 treatment exhibiting the most pronounced effect. Foliar application of TiO2 at the S1 stage significantly increased the number of florets and spikelets, improved grain setting rates, and consequently boosted the grain number per spike. Application of TiO2 during the S2 stage significantly enhanced grain filling rates, thereby increasing thousand-grain weight and achieving yield improvement. T2 demonstrated optimal performance under both conditions, enhancing grain storage capacity and morphological traits. This approach not only increased late-sown wheat yields but also improved grain quality indicators such as protein content, wet gluten, and sedimentation value. Therefore, applying 501 μmol L-1 (T2) TiO2 during the booting stage (S1) appears to be effective for achieving high yields and superior quality in late-sown wheat.