ALLELIC DIVERSITY IN GLOBAL MAIZE GERMPLASM AND IMPLICATIONS FOR UTILIZATION

¹ CIMMYT, Int. Apdo Postal 6-641 06600 Mexico, D.F. Mexico

² 7 La Feuillee 44260 La Chapelle-Launay, France

³ National Maize Improvement Center of China, China Agricultural University, Yuan Ming Yuan West Road No. 2, 100094 Beijing, China

Allelic diversity at expressed loci has been the basis for crop improvement via selection by breeders and farmers for thousands of years. Allelic diversity at neutral marker loci has frequently been correlated to pedigree relationships, geographic origin, seed maintenance methods, and even in some cases, to morphological diversity and heterosis. The assumption that allelic diversity at neutral marker loci reflects diversity at expressed loci has frequently proven correct. The International Maize and Wheat Improvement Center (CIMMYT) is using SSRs and other molecular markers to characterize the numerous maize inbred lines, breeding populations, and landraces available in its genebank and breeding programs. Allelic diversity present in the tropical lines was found to be higher than in temperate lines, although the Polymorphic Information Content (PIC) values were similar. This indicates a high number of rare allelic variants in the tropical germplasm. The number of alleles and PIC values in CIMMYT breeding populations and Mexican landraces were similar, and considerably higher than those reported in inbred lines (temperate and tropical). Maize populations and landraces from the USA, Mexico, Central and South America, the Caribbean, and Europe showed patterns of diversity in many cases reflecting known trade routes, and in other cases showing previously unknown introductions into new areas. Despite the lower numbers of alleles in the temperate vs. tropical maize, some alleles were found almost exclusively in temperate maize.