Maize (Zea mays L.) is one of the most important crops worldwide. However, low temperature limits seed germination and seedling growth of maize, which can in turn affect grain yield. The calcium ion (Ca2+) is the second messenger involved in the response to environmental-stimuli-induced signal transduction networks. The underlying physiological mechanisms related to the effects of exogenous Ca2+ treatment of different maize cultivars under low temperature are unclear. We selected two inbred lines, cold-sensitive cv. C546 and cold-tolerant cv. Y478, for studying the effects of Ca2+ on seed germination, photosynthesis, antioxidant enzymes and the osmotic regulation of seedling resistance to low temperature. The optimal concentration of CaCl2 was 80 mmol L–1, which significantly improved the germination percentage at temperatures <10°C. Application of CaCl2 at this concentration under cold stress mitigated the degree of membrane injury and improved the antioxidant enzyme system through reduced relative electrolyte conductivity and malondialdehyde content, increased the soluble protein content, and enhanced superoxide dismutase and peroxidase activity. CaCl2 also significantly increased chlorophyll fluorescence indicators (Fv/Fo, Fv/Fm) and the photosynthetic rate. We conclude that exogenous CaCl2 at a concentration of 80 mmol L–1 protects the function and structure of the membrane and photosystems, improves antioxidant enzyme activity and increases osmotic regulatory substances under cold stress. These results improve our understanding of the mechanisms of Ca2+ and contribute to the development of cold-tolerant maize varieties.

Southern corn rust (SCR) is one of the most destructive foliar diseases in maize (Zea mays L.), resulting in significant yield losses. Therefore, the continuous identification of disease-resistant germplasm and the deployment of resistant hybrids is essential for durably controlling SCR. The objective of this research was to identify and characterize resistance loci against SCR in maize to expand disease management strategies. Here, we identified a maize landrace with high resistance to SCR ‘Silunuo’ (SLN) approaching complete immunity. We backcrossed it with a susceptible inbred line, N531, to generate a stable SCR-resistant introgression line N531_R. By crossing it with F35 (a susceptible inbred line), we created a large F₂ segregating population and mapped a major SCR-resistant locus on chromosome 10, known as RppSLN. Based on the genome assembly and annotation, we found that RppSLN harbors two NBS-LRR (nucleotide binding site–leucine-rich repeat) genes, namely Zmays10G000430 and Zmays10G000440. These NBS-LRR genes were significantly induced during artificial inoculation with Puccinia polysora, suggesting that they might be candidate genes collectively contributing to the resistance level at this locus. In conclusion, this study identified a major SCR resistance locus directly isolated from a landrace, providing valuable support and information for expanding new disease-resistant germplasms and promoting the utilization of landraces.