Molecular analysis of white clover population structure in grazed swards during two growing seasons

White clover (Trifolium repens L.) populations persist for years in grazing lands primarily through clonal growth, yet retain high genetic variability . This study was conducted to determine how clone structure dynamics affect ed intraspecific genetic variation of white clover at three pasture sites. Up to 37 trifoliate leaf samples were taken monthly by resampling specific points in four 1.2 x 1.2 m area quadrats from April to September for 2 yr; random amplified polymorphic DNA (RAPD) profiles of 1160 and 973 samples, i n 1997 and 1998, respectively, were analyzed. Significantly more clones wer e sampled in 1997 (162) than in 1998 (58) (P < 0.0001). The majority of clo nes were not detected more than once during each year. The soil water conte nt was significantly lower in 1998 than in 1997 (P < 0.0001). The number of sampled clonal members in quadrats ranged from 0.5 to 12.8 across both yea rs on the three pastures. Within-population analysis of molecular variances (AMOVA) by date for the three pastures ranged from 15 to 74% and 46 to 80% in 1997 and 1998, respectively, indicating low to medium genetic diversity in the populations. The fraction of clonal samples relative to the total n umber of samples ranged from 0.03 to 0.78 in 1997 and 0.04 to 0.33 in 1998. Higher numbers of clonal members appeared to reduce genetic diversity; how ever, this was offset by rapid turnover of clones. We conclude that genetic variability of white clover is dynamic at the local scale, which contribut es to its long-term persistence in grazing lands.