Genetic Variation within among White Clover Populations from Managed Permanent Patures of the Northeastern USA

Abstract

White clover (Trifolium repens L.) population dynamics and genetic variation were characterized in populations under continuous grazing management. RAPD (random amplified polymorphic DNA) profiles were developed for individuals sampled from managed permanent pastures on 18 farms in Pennsylvania (PA), New York (NY), and Vermont (VT). Genomic DNA from individual white clover plants (48) sampled over two transects at each location during fall, 1996, was amplified by the PCR (polymerase chain reaction). RAPD profiles of 54 RAPD markers were used to compute genetic distances between pairs of individuals. The data set for each location was evaluated by AMOVA (Analysis of Molecular Variance), which apportioned total variation among individuals within populations, among populations within states (PA, NY, VT), and among state populations (PA, NY, VT). An interpopulation distance matrix of 18 fall‐sampled populations was used to calculate a dendrogram. Two groups of 6 and 10 populations were evident, with two populations as single branches. VT populations were in the larger population group, and the PA and NY populations were in both groups. White clover genetic variability in the swards was higher than expected, all populations were significantly different (P < 0.001) from each other, and the PA, NY, and VT populations were indistinguishable from each other. Populations from four PA locations also sampled in summer changed significantly two months later in the fall. Rapidly changing white clover diversity may be due to rapid, differential growth of individuals best adapted to seasonal changes in the microenvironment, or to unexpectedly high levels of seedling recruitment.