Morphological characterization of native maize populations of the ratón race from Coahuila, Mexico
Because of its wide distribution and adaptation, the maize Ratón race (Zea mays L.) is an important component of the diversity in the state of Coahuila, Mexico. The objective of the present research was to perform a morphological characterization of 83 native populations of the Ratón race and identify a subset that will represent diversity. Populations were evaluated in replicated experiments at two different locations with two planting dates per location. Twentysix quantitative characters of the plant, tassel, ear and grain were recorded, and 14 additional characters (indices) were calculated as relationships among characters. Phenotypic diversity was examined by principal component and cluster analyses. Differences (p ≤ 0.01, p ≤ 0.05) among environments were found for 28 characters and (p ≤ 0.01) among populations for all characters, due to variation in environments and diversity among populations, respectively. Also, differences were found (p ≤ 0.01, p ≤ 0.05) in 38 of the 40 characters in the populations × environments interaction, as a differential response of the populations in the environments. Based on the repeatability index (r > 1.0), 10 characters and nine indices less influenced by the environment were selected for classification. The first two components explained 53.3% of the total variation and it was established that the vegetative, ear and tassel characters were the most important in describing the variation; this allowed to identify a pattern of diversity associated with the area of adaptation of populations in low – intermediate – transition areas, which reveals that maize variation is closely related to altitude, and temperature and humidity gradients. Based on the dendrogram, a representative subset of the diversity of the Ratón race in Coahuila was obtained, made up of 13 of 83 populations (15.7%).