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GENOMICS, MOLECULAR GENETICS & BIOTECHNOLOGY

Spatiotemporal Genetic Structure within White Clover Populations in Grazed Swards

USDA-ARS, Pasture Systems and Watershed Management Research Unit, Curtin Road, Building 3702, University Park, PA 16802-3702

* Corresponding author (d3g{at}psu.edu)

White clover (Trifolium repens L.) populations exhibit high genetic and clonal diversity, but often exist for many decades in grazed swards at northern midlatitudes. This study was conducted to determine whether genetic structure exists within rapidly changing populations and is a factor in creating genetic diversity. Trifoliate leaf samples were taken monthly in 1997 and 1998 from up to 37 specific points in four 1.2- by 1.2-m quadrats from May to September on two central Pennsylvania farm sites. Random amplified polymorphic DNA (RAPD) profiles of population samples from 67 quadrats were tested by spatial autocorrelation analysis based on a multivariate nonparametric approach. Significant (P < 0.05) overall spatial autocorrelation was found in 26 populations that had clones and in seven populations without clones, while nonsignificant autocorrelation was found in 27 and seven populations with and without clones, respectively. Frequencies of significant autocorrelation for populations on one site in 1997 and 1998 were 0.5 and 0.2, respectively, and the frequencies for the other site were 0.8 and 0.4, respectively. The ratio of populations lacking significant autocorrelation to those with significant autocorrelation changed little from zero to six clones, but increased dramatically for seven or eight clones. The estimated patch size (overall mean 66 cm; SE = 8) for two years and two sites did not change significantly over the growing season. Number of clones and patch size was less important in determining genetic structure than variable existence of spatial autocorrelation.

Abbreviations: RAPD, random amplified polymorphic DNA