Sampling strategy to develop a core collection of Uruguayan maize landraces based on morphological traits

Core collections were suggested to improve germplasm utilization. A core collection is a subset chosen to represent the diversity of a collection with a minimum of redundancies. Because diversity is distributed between and within groups with different degrees of organization, an adequate classification of accessions into related groups should be performed prior to the selection of a core collection. Different classification strategies for the Uruguayan Maize Collection were compared, and the best one was used to select a core collection. The following classification strategies were compared following a multivariate approach using the available maize data base: i) racial classification, ii) geographic origin (south and north of the country), and iii) a combination of kernel type and geographic origin. The third option was considered the best classification rule, since it takes into account two points which are closely related to the distribution of diversity: genotypic composition and geographic origin. The following five groups were identified in the collection: a) pop, b) floury, c) dent, d) southern flint-semiflints, and e) northern flint-semiflints. Eight core collections, each of 90 accessions, were selected, using different strategies to weight the groups in the core and to select the accessions from the groups. The P, C, and L strategies were used and combined with either random selection within the group or the Relative Diversity method. Two samples of 90 accessions were obtained at random without considering the classification. The Relative Diversity method combined with the L strategy produced the best core collection, as it retained the highest percentage of the ranges for the 17 variables included in the analysis. On average, 91% of the ranges were retained in the core, confirming its representativeness.