Interspecific hybridization in the genus Trifolium

The genus Trifolium (Leguminosae) or clovers includes a number of agriculturally important forage species. In particular Trifolium repens (white clover) and Trifolium pratense (red clover) are widely used in temperate livestock agriculture. Interspecific crossing programmes within this genus have been carried out for more than 50 years, in many cases involving embryo rescue or ovule culture techniques. In general, the aims of these have been twofold: to aid understanding of evolutionary relationships within the genus and to introgress useful traits, predominantly into white or red clover. In the case of white clover, the greatest efforts have been made with respect to crossing with Trifolium nigrescens and Trifolium ambiguum. Novel germplasm has been developed and useful traits transferred, although no material has yet been commercialized. The main emphasis with respect to red clover has been increasing longevity through crosses with more persistent species, particularly Trifolium medium. Again, this work has not yet resulted in new varieties. Wider crossing programmes, allied in recent years to comparisons at the DNA level, have shed considerable light on the systematics and evolution of the genus. The future of interspecific hybridization for improvement of the agriculturally important clovers and the role of molecular approaches in this are discussed