Germplasm Diversity among Cultivars and the NPGS Crimson Clover Collection

Abstract

Crimson clover (Trifolium incarnatum L.) is a cool‐season annual forage legume. Few morphological traits are recorded to distinguish genotypes and very little is known about its genetic diversity. The objective of this research was to classify and characterize the genetic diversity in the USDA‐ARS National Plant Germplasm System (NPGS) accessions and USA and European Economic Community (EEC) cultivars. Descriptions of EEC cultivars and their breeding histories are also presented. A secondary objective was to determine if T. incarnatum vat. molinerii (Baib. ex Hornem.) Ser. should be considered a distinct species. Genomic DNA from leaves of 37 taxa was examined in 1993 by the polymerase chain reaction (PCR) using 29 random amplified polymorphic DNA (RAPD) markers. Plants grown in the greenhouse were also observed for inflorescence color and relative flowering time. Cluster analysis of pairwise means of RAPD maker distances and cultivar pedigree histories revealed similar genetic backgrounds among most cultivars. Flower color was associated with RAPD marker grouping (P ≤ 0.02) but flowering time was not (P ≤ 0.31). Bolh red vs. non‐red inflorescence color and early‐ vs. late‐flowering traits could be predicted by specific RAPD bands (95 and 93% accuracy, respectively). Analysis of internal transcribed spacer region sequences (ITS) from ribosomal DNA (rDNA) showed diverse crimson clover taxon to be more similar to one another than to var. molinerii (0.4 and 0.9% base pair differences, respectively; P ≤ 0.001). Because of the limited diversity within the current NPGS collection, additional accessions should be collected, morphologically evaluated, and genetically analyzed to broaden the genetic base of the collection. Crimson clover var. molinerii is a sister taxa of more typical crimson clover accessions but exhibits enough ITS diversity to be classified as another species.