Early Sowing Approach for Developing Climate Resilient Maize: Cold Stress Impact on Germination of Adapted Inbred...

In temperate regions, early sowing of high nutritive genotypes could support maize production sustainability by avoiding warming-related unfavorable environment conditions during flowering. Seven standard maize (SM) lines and their nine quality protein maize (QPM) counterparts were evaluated for cold tolerance during germination. Cold stress (13°/6 °C) was applied for five days, after a 48 h imbibition period under optimal temperature (25°/22 °C). Germination, physiological parameters, and some primary and secondary metabolites in the seeds were analyzed. No significant differences (p > 0.05) were observed in cold tolerance between SM and QPM. Cold stress significantly reduced germination energy (SM-p < 0.05, QPM-p < 0.001) and physiological traits (p < 0.001), with shoot traits being most severely affected. The potentially high impact of gallic (p < 0.001), protocatechuic (p < 0.05), and p-coumaric (p < 0.001) acids on germination under stress and negative effect of lutein + zeaxhantin and β-cryptoxhantin (p < 0.05) on root length was revealed. Among all lines, L3QPM excelled under stress, with unchanged germination energy and the lowest fold change in vigor indices (0.35 for VI1, 0.45 for VI2). Also, β + γ-tocopherol and gallic and caffeic acids were significantly higher (p < 0.05) compared to its SM original. Lines L1QPM2, L3QPM, and L7QPM, combining improved nutritional quality with high cold tolerance, will be incorporated in further early sowing research and breeding programs.