| The size and heterogeneity of world germplasm collections have hindered their evaluation and utilization. It has been suggested that germplasm collections could be reduced to a core collection, which is a condensed representation of the genetic diversity of a crop species and its relatives. The objectives of this research were to evaluate selection procedures for designating a core collection for US Alfalfa Plant Introductions. A data file was developed for 50 agronomic, forage quality, root and crown morphology, pest resistance, and stress tolerance traits for 1,100 perennial Medicago Plant Introductions (P.I.'s) collected from 47 countries. The 1,100 accessions were classified into 18 groups based on number of accessions per country and by geographical proximity. Eight alternative methods for developing a 200-entry core were compared by non-parametric procedures to the original P.I. collection. The methods included the utilization of multivariate procedures, random or directed selection of entries, the combination of both, and a totally randomly selected core. The sign test was used to compare the means and the variances for 38 traits having the most complete data sets among the cores developed by the eight methods. None of the alternative methods changed the trait means; but nearly all methods, with the exception of the randomly selected core, significantly increased the variance for most traits. Two methods appeared to be the best alternatives for designating core collections. These included method 3 (combining cluster analysis on principal components within each geographical group with random selection of entries within each cluster) and method 8 (directed selection of entries within each geographical group). Method 3 needs a complete data set and extensive computer facilities. Method 8 can utilize incomplete data sets and does not require computer facilities. I choose method 8 for designating the core for perennial Medicago spp. P.I.'s because it provided the greatest variability for all traits. This 200-entry core is the first one designated for any crop in the Germplasm Resources Information Network (GRIN) System. |
