White clover

White clover (Trifolium repens) is an important forage legume of temperate pastures. It is an outbreeding allotetraploid species (2n=4x=32) characterised by its stoloniferous habit. The benefits of white clover in terms of nitrogen fixation, quality of forage and effect on animal performance are well known. Breeding programmes across the world have focused on increased persistency and the contribution that white clover makes to mixed swards with grasses. A critical component of this is a dense stolon network. White clover varieties are classified according to leaf size with small leaf types suitable for continuous sheep grazing and large leaf types appropriate for rotational grazing or silage. Improvement is increasingly focused on improving the efficiency of resource use and on adapting to climate change. Molecular approaches have developed in white clover over the last 10 years including genetic maps, expressed sequence tag (EST) libraries and bacterial artificial chromosome (BAC) libraries. The model legume Medicago truncatula is closely related to clover and work on this species is generating key resources for translational genomics. An important recent development is work suggesting that the modern day species Trifolium occidentale and Trifolium pallescens are likely to be closely related to the diploid ancestors of white clover and this has opened the way for the development of subgenome-specific molecular markers facilitating marker-assisted breeding.