Variation among Andean races of maize for cold tolerance during heterotrophic and early autotrophic growth.

Cold in the initial growth stages is an important stress factor for maize grown in regions with a temperate climate, particularly in case of early sowing. Sources of tolerance have been identified in adapted genotypes, but promising genes for cold tolerance should also be found in material developed under the lower-temperature margins of the crop distribution. This research was conducted in order to test Andean maize accessions for cold tolerance expressed during both the heterotrophic and early autotrophic growth stages. Experiments were conducted in controlled environments to study cold tolerance traits (germination %, germination index and plant growth rate) at continuous 10°C (heterotrophic growth) and at varying 10-16°C (autotrophic growth). An experiment was also performed in the field with early sowing (both heterotrophic and autotrophic growth). In each experiment, a control trial was conducted in more favorable conditions (i.e. continuous 25°C in a controlled environment or late planting in the field) so that cold tolerance traits could also be examined as the ratio between the stress and the control trial. None of the accessions was superior for all cold tolerance traits. However, several Andean maize accessions outperformed the US Corn-belt hybrid checks for one or more traits, both in heterotrophic and autotrophic growth. Overall, BOZM 855, PMS 636, Poblacion D, Poblacion E and BOZM 696 were the best accessions, suggesting that they can be a promising source of genes for improving cold tolerance of adapted maize genotypes.