Cytogenetics, genetic diversity and phylogenetics of wild Zea species, with emphasis on Zea nicaraguensis

Maize (Zea mays subsp. mays) is a member of the grass family Poaceae (Gramineae), together with many other important agricultural crops. The wild species commonly known as teosintes are the closest relatives of maize. Teosintes are wild grasses with a native distribution area from Mexico to Nicaragua and are an important genetic resource for maize improvement. Teosinte from Nicaragua (Zea nicaraguensis) is to a large extent an unutilized genetic resource and its properties in terms of desirable traits, such as water-lodging adaptation and disease resistance have to be phenotypically and genetically characterized.The aims of this thesis were to verify the chromosome number and characterize the genetic diversity of Nicaraguan teosinte populations and to determine genetic structure, gene flow, morphological variation and phylogenetic relationships among Meso-American teosintes. The thesis includes results from cytological, genetic, morphological and phylogenetic studies. Cytogenetic studies were based on C-banding techniques. Microsatellite (SSR) markers and DNA sequences of cpDNA regions were used for genetic diversity and phylogenetic studies respectively, whereas morphological studies involved various quantitative morphological traits. The C-banding pattern revealed that Z. nicaraguensis is more similar to Z. luxurians than other teosintes and cultivated maize. Among the Meso-American teosintes, Z. diploperennis, Z. perennis and Z. nicaraguensis showed the highest values in the number of rare and unique alleles and the data also indicated that the gene flow between Z. nicaraguensis and Z. luxurians has been more frequent than between other teosintes. The morphological characterization revealed that the traits of the number of lateral branch nodes bearing ears, the glume width, the number of tiller nodes bearing ears and the number of tillers per plant were the most important in discriminating between taxa and the principal component analysis grouped many traits around the Z. nicaraguensis, Z. luxurians and Z. mays subsp. huehuetenangensis. Finally, the variation among cpDNA sequences was not enough to give a definitive phylogenetic resolution among the five Zea species, but even so our results support the idea that Z. nicaraguensis could be treated as a separate species distinct from Z. luxurians.