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 (<i>SPAD</i>) and spectroscopic indices (<i>CHI</i>, <i>PRI</i>) in wheat flag leaves, markedly improved the net photosynthetic rate, and increased the activities of antioxidant enzymes (<i>SOD</i>, <i>POD</i>) while reducing the accumulation of membrane lipid peroxidation products (<i>MDA</i>), 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.