A Description and Interpretation of the NPGS Birdsfoot Trefoil Core Subset Collection

Systematic evaluations for a range of traits from accessions in National Plant Germplasm System (NPGS) core subset collections should assist collection management and enhance germplasm utilization. The objectives of this research were to: (i) evaluate the 48-accession NPGS birdsfoot trefoil (Lotus corniculatus L.) core subset collection by means of a variety of biochemical, morphological, and agronomic characters; (ii) determine how these characters were distributed among the core subset accessions and associations among plant and ecogeographic characters; (iii) define genetic diversity pools on the basis of descriptor interpretive groups; and (iv) develop a method to utilize the core subset as a reference collection to evaluate newly acquired accessions for their similarity or novelty. Geographic information system (GIS) databases were used to estimate the ecogeography of accession origins. Interpretive groups were constructed to describe the range of core subset descriptor variation by cluster analysis and verified by discriminant analysis. Associations among plant descriptors and with ecogeographic characteristics were determined by Pearson's correlation coefficients or the Mantel Z statistic. The accessions were classified into four distinct genetic diversity pools that were described by plant traits and ecogeographic origins. The core subset used as a reference collection successfully classified three unique accessions not originally included in the core subset. This approach identified germplasm that was different from that present in most North American cultivars and can be used to evaluate future acquisitions. The concepts of interpretive groups, genetic diversity pools, and reference collection comparisons should be applicable for assessing and managing other core subset collections.