Genetic variation in physiological discriminators for cold tolerance-early autotrophic phase of maize development

Earlier spring planting to maximize the duration of the growing season has increased the importance of early-season cold tolerance in maize (Zea mays L.). The objectives of this study were to assess the response of several physiological parameters associated with cold tolerance in maize during early autotrophic development and to quantify variability in the response to cold stress among 49 maize inbred lines. At the 7-leaf tip stage, maize inbred lines were subjected to two day/night temperature regime treatments, 25/15degreesC (control) and 15/3degreesC (cold). Carbon exchange rate (CER), leaf chlorophyll content, quantum efficiency of Photosystem II, leaf conductance, dry weight, root/shoot ratio, and rate of development were measured at the 8-leaf tip stage for genotypes under both treatments. The cold treatment effects were significant for all parameters except root/shoot ratio. Genetic diversity for most traits investigated was observed for the response of the inbred lines to cold stress. Results of this study show that leaf CER and rate of development are good discriminators of cold tolerance during early phases of development.