Variation amongst Survivor Populations of Two White Clover Cultivars Collected from Sites across Europe: Morphological and Reproductive Traits

A single-site field experiment was carried out to investigate differences in quantitative traits between survivor and original baseline populations of two white clover cultivars (AberHerald and Grasslands Huia). The survivor populations had been generated from vegetative samples collected after growth for 2–3 years at a range of sites across Europe. The aims of the experiment were to determine the extent of genetic shift due to selection in these populations compared with the baseline material; to relate the nature of any genetic shift that occurred to the environments in which the selection operated; and to determine whether the survivor populations formed distinct groups. Directional selection occurred in many traits in populations of each cultivar. Correlation analysis was carried out to determine the influence of basic climatic variables at each site on traits of the survivors. Few correlations were found, except for a tendency for flowering date in Grasslands Huia to be delayed in sites with cold winters and high levels of radiation in the summer. Multivariate analysis showed that in each cultivar the populations from Finland were distinct from all others and conformed to a typical ‘northern European’ morphology. Analysis of the variation within survivor populations showed that stabilizing selection had not operated at any site, even those with extreme climates. For the range of traits measured, the survivor populations had not reached an equilibrium between their genetic structures and the selective forces acting upon them.