HIGHLAND MAIZE FROM CENTRAL MEXICO - ITS ORIGIN, CHARACTERISTICS, AND USE IN BREEDING PROGRAMS

The races of maize (Zea mays L.) which are cultivated in the highlands of central Mexico at altitudes above 2000 m include Palomero Toluqueno, Conico, Arrocillo Amarillo, Chalqueno, and Cacahuacintle. This complex of races is of ancient origin and has a distinct plant morphology, karyotype, and isozyme frequency compared to other types of maize except, possibly, some races from the highlands of Guatemala. It is adapted to cool areas with mean growing season temperatures between about 12.5 and 17.0 degrees C and is superior to maize from temperate, mid altitude tropical, and lowland tropical regions for seedling emergence, photosynthetically-based growth, and ability to continue grain filling at low temperatures. It also has better frost and hail tolerance, but is poorly adapted to high temperatures. It can emerge from sowing as deep as 0.25 m, and is resistant to rust caused by Puccinia sorghi Schw. With the support of the Mexican government, hybrids and improved open-pollinated cultivars have been derived from these races. CIMMYT is conducting a breeding program based on these races for tropical highlands worldwide, but with the inclusion of other germplasm to improve grain yield and agronomic traits, especially resistance to lodging. These programs have shown excellent prospects for improving grain yield and agronomic traits in highland tropical environments. Research from New Zealand suggests that this germplasm resource has potential for raising grain yields in cool, temperate environments.