Botanical and Genetic Change in Grass-clover Based Systems

Swards based on grass-clover mixtures are regaining importance in grassland production in Flanders. The population structure in these swards develops in response to abiotic and biotic stresses. In this study we analysed botanical and genetic change in grass-clover mixtures. We have screened 15 varieties of white clover (Trifolium repens L.) and 15 varieties of red clover (Trifolium pratense L.) by amplified fragment length polymorphism (AFLP) markers. We selected five varieties of each of the species with high genetic distances between them. We set up a field experiment with these clover varieties in mixture with perennial ryegrass. The plots were mown during the growing seasons of 2006, 2007 and 2008 and the botanical composition was analysed at the last cut of each year. The proportion of the grass was low in the mixtures with red clover. The percentage white clover was low in the mixtures with both legumes in the first years. Since red clover is not persistent white clover was expanding in these plots in 2008. In August 2008 we took samples to test the genetic shift in the white and red clover varieties growing in association with perennial ryegrass. The genetic diversity decreased in all varieties.