Effects of Uniconazole-Sucrose on Lodging Resistance and Lignin Accumulation of Two Contrasting Wheat Genotypes from Different Periods Under High Temperature Stress

Elevated temperatures due to global climate change adversely affect plant growth and development, which has become a major factor restricting wheat (Triticum aestivum L.) production. Despite the introduction of dwarfing genes that have enhanced lodging resistance as well as productive potential in wheat breeding, lodging still affects wheat yields. Plant growth regulators are widely recognized as effective agents in mitigating crop lodging. Few studies have investigated the high-temperature lodging sensitivity of wheat genotypes from different breeding periods, nor have they examined how uniconazole-sucrose regulates lodging resistance under heat stress. To fill this research gap, an experiment was conducted in which two contrasting wheat genotypes from different periods, Bima 1 (BM1, ~135 cm tall, a historical genotype released in 1953, lodging-susceptible) and Shannong 28 (S28, ~75 cm tall, a modern genotype released in 2014, lodging-resistant), were exposed to high temperature stress combined with uniconazole-sucrose application. The results showed that high-temperature-induced increases in plant gravity center height, together with decreased stem diameter coefficient, stem plumpness, and lignin deposition, were the main factors responsible for the reduction in bending section factor and mechanical strength of wheat stems. These modifications are associated with reduced lodging resistance, increased susceptibility to lodging, and significant yield losses. Nevertheless, exogenous application of uniconazole-sucrose lowers plant gravity center height, enhances stem diameter coefficient, stem plumpness, and lignin content, thus alleviating lodging risk and boosting wheat yield under high temperature stress. High temperature stress was associated with downregulated relative expression levels of key genes involved in lignin metabolism and reduced activities of the corresponding key enzymes, as well as inhibited lignin biosynthesis and accumulation in stems and increased incidence of wheat lodging. Conversely, foliar spraying of uniconazole-sucrose alleviated these suppressive effects on lignin biosynthesis, thus enhancing stem mechanical strength and reducing the lodging index of wheat. Moreover, these indicators were more sensitive to heat stress or uniconazole-sucrose treatment in BM1. The two genotypes examined suggested a potential trend that S28 may exhibit reduced sensitivity to high temperature in terms of mechanical traits and lignin synthesis, which could contribute to enhanced lodging resistance under heat stress.