Agronomic Evaluation of Latin American Maize Accessions

Use of photoperiod‐sensitive tropical germplasm for breeding in temperate regions is hampered by several problems. The inability to accurately evaluate photoperiodically sensitive accessions under long‐day conditions leads to an inability to choose the best available materials. The use of short‐day seasons in Homestead, FL, and Weslaco, TX has been investigated for the screening of the available set of typical accessions of the Latin American maize ( Zea mays L.) races. Nursery data were used to select about 400 better accessions from a set of some 1300 typical accessions. Replicated trials under short‐day conditions, which for maize act as day‐neutral conditions, were used to screen the selected accessions, with temperate and tropical hybrids used as standards for comparison. Yield distributions of the tropical accessions were symmetric under short‐day conditions (in Florida and Texas), but highly skewed toward zero under longday conditions (in North Carolina) for all but the earliest maturity group. When yields and differences in male and female flowering times were plotted against latitude, distinctly different patterns were observed under long‐ and short‐day conditions. Under long‐day conditions, yields were greatly depressed, and differences between male and female flowering greatly increased for accessions originally collected between 15 °C N and 15 °C S latitude, as compared to results under short‐day conditions, where both yields and male vs. female flowering differences had largely linear regressions on latitude, with slopes near zero. Under short‐day test conditions, it was possible to identify races of maize and specific geographic regions as promising sources of tropical maize germplasm for temperate breeding programs.