Diverse coping modes of maize in cool environment at early growth.

backgroundMaize cultivation has considerably expanded beyond its place of origin in Central America. The successful adaptation of maize to temperate climates can be achieved by selecting genotypes that demonstrate tolerance to low temperatures, especially in cold springs. In maize, cold tolerance at the early growth stages enables early sowing, a long growing season, and eventually high yields, even in temperate climates. Maize adaptation during early growth has not been thoroughly investigated; therefore, we tested the working hypothesis that several distinct and independent adaptation strategies may be involved in maize habituation to cool temperate climates during seedling establishment.

resultsWe studied the effect of mild cold stress (day/night 16/12 °C) on early growth stage followed by regrowth at optimal daily temperatures (24/21 °C). Automated plant phenotyping was performed on 30 inbred lines selected from a diverse genetic pool during preliminary studies. As a result, we generated time series based on selected morphological parameters, spectral parameters, and spectral vegetation indices. These curves were clustered and four classes of maize with clearly contrasting growth modes and changes in their physiological status were distinguished at low temperatures and during regrowth. Two classes comprised either cold-sensitive (slow growth and poor physiological status in cold) or cold-tolerant (moderately fast growth and good physiological status in cold) lines. However, two other classes showed that growth rate and physiological status at low temperature is not necessarily related, for instance one class included lines with small seedlings but good physiological status and the other grouped seedlings with rapid growth despite poor physiological status. These classes clearly exhibited different modes of cold adaptation. Moreover, a class containing cold-sensitive inbred lines may represent a distinct and novel type of cold-adaptation strategy related to the arrest of coleoptile emerge related with ability to recover rapidly under favourable conditions.

conclusionsOur results support the hypothesis that maize may have several adaptation strategies to cold environments at early growth stages based on independent mechanisms. These findings suggest that maize adaptability to adverse environments is likely more complex than previously understood.