Evaluation of Improved Maize Populations in Mexico and the U.S. Corn Belt 1

Genetic variabiltiy is essential for continued genetic improvement of any crop species. One potential sourse of genetic variability is the use of exotic or unadapted germplasm. Although considerable genetic variability may be available in germplasm repositories, indiscriminate introduction of exotic germplasm may lower the breeding value of elite, adapted populations. Exotic germplasm that has been improved by cyclical selection should reduce some of the detrimental effects of incorporating exotic sources into adapted sources. The objective of our study was to determine the relative yields of maize ( Zea mays L.) populations developed by recurrent selection in Mexico and in the United States. Trials were conducted in each country to determine the response of the populations per se and their population crosses. The U.S. Corn Belt populations performed better in Mexico than did the Mexican populations in the U.S. Corn Belt and some of the Mexican by U.S. Corn Belt population crosses tested in Mexico did not differ from the check hybrid. The U.S. Corn Belt populations showed better adaptation to Mexican environments than the Mexican populations did to U.S. Corn Belt environments. Of the populations tested, BS13(S)C2, derived from ‘Stiff Stalk Synthetic’ after nine cycles of recurrent selection for yield, had the highest general combining ability with the improved Mexican populations. Thus, it appeared that U.S. Corn Belt populations could be sources of useful alleles for yield, earlier maturity, and shorter plant height for Mexican breeding programs located in tropical and subtropical areas. None of the Mexican populations per se or their crosses approached the yield of the check hybrid when tested in the U.S. Corn Belt; most were taller, flowered later, and had higher grain moisture at harvest.