Objective  Three cold-tolerant sweet maize cultivars were tested at seedling stage as well as in the field to select the variety for extending growth season to increase productivity.

  Method  An indoor experiment using seedlings of Mintian 6855, Cuitian 618, and Guangliangtian NO. 27 (named Guangliang 27) was conducted at 4 ℃ for varied durations. A field test was also carried out on the plants in cold weather. Phenotype identification was used to compare and analyze the physiological indices on the seedlings and the ear appearance in the field.

  Results  (1) Phenotypic appearances of Mintian 6855 seedlings of the 3 cultivars showed the strongest cold tolerance after being treated at 4 ℃ for 24, 48, and 72 h, while Guangliang 27 seedlings were the weakest. (2) The activities of SOD, CAT, and POD of the Mintian 6855 seedlings in 48 h were respectively 315.43 U·g⁻¹, 771.97 µmoL·min⁻¹·g⁻¹, and 429.81 U·g⁻¹; 13.9%, 28.5%, and 109.1% higher than those of Cuitian 618; and 34.3%, 18.8%, and 86.4% higher than those of Guangliang 27. Among the 3 cultivars, Mintian 6855 accumulated MDA in the least amount. The SP content in Mintian 6855 was significantly higher than that in Guangliang 27. (3) The SOD activity was extremely significant correlated with the treatment time. The CAT and SOD activities significantly correlated with the SP content. (4) In the field test, the well-developed ears harvested from the winter crop of Mintian 6855 had an appealing appearance free of any missing kernels. On average, the plants produced significantly more rows of kernels at 15.6 and dry kernel yield at 71.68% per ear than did Cuitian 618 or Guangliang 27.

  Conclusion  Mintian 6855 was significantly more tolerant to low temperatures as shown phenotypically and physiologically at seedling stage. As a mature plant in the field, it bore appealing ears under cold climate.