Phylogenetic Relationships among North American Popcorns and Their Evolutionary Links to Mexican and South American Popcorns

To determine genetic relationships among representative popcorns (Zea mays L.) of the New World, 56 maize populations from the USA and nine Latin American countries were characterized for 29 morphological traits, 18 isozyme loci, and 31 SSR loci. Cluster and principal component analyses were performed upon standardized morphological data and allelic frequencies from isozyme and SSR loci to elucidate relationships among populations within a geographical and historical context. Three groups of popcorn, with distinctive morphological characteristics and genetic profiles, were identified in the North American populations. The first group includes the North American Yellow Pearl Popcorns, which are currently the most important for U.S. commercial production. This group could be derived from introductions of the race Curagua from Chile into New England in the 19th Century. The second group includes the North American Pointed Rice Popcorns, which probably originated from the complex of traditional races of pointed popcorns from Latin America, such as Palomero Toluqueño, Confite Puntiagudo, Canguil, and Pisankalla, which diffused from the highlands of central Mexico into northern Mexico and then into southwestern USA. The third group includes the North American Early Popcorns, which show a marked influence of Northern Flint maize, from which they probably acquired the trait of early maturity. This third group also shows genetic influences of maize from northwestern Mexico and even from early European varieties of popcorn introduced late in the 19th Century. We propose that the three groups of North American popcorn identified in this study be recognized taxonomically as distinct races, and we provide characteristic traits as well as isozyme and SSR alleles to define the new races.