HIGHLAND MAIZE FROM CENTRAL MEXICO - ITS ORIGIN, CHARACTERISTICS, ANDUSE 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 Toluquen o, Conico, Arrocillo Amarillo, Chalqueno, and Cacahuacintle. This comp lex of races is of ancient origin and has a distinct plant morphology, karyotype, and isozyme frequency compared to other types of maize exc ept, possibly, some races from the highlands of Guatemala. It is adapt ed to cool areas with mean growing season temperatures between about 1 2.5 and 17.0 degrees C and is superior to maize from temperate, mid al titude 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 Sch w. With the support of the Mexican government, hybrids and improved op en-pollinated cultivars have been derived from these races. CIMMYT is conducting a breeding program based on these races for tropical highla nds worldwide, but with the inclusion of other germplasm to improve gr ain yield and agronomic traits, especially resistance to lodging. Thes e programs have shown excellent prospects for improving grain yield an d agronomic traits in highland tropical environments. Research from Ne w Zealand suggests that this germplasm resource has potential for rais ing grain yields in cool, temperate environments.