Interspecific hybrids have been developed between white clover and the annual, profuse flowering diploid species Trifolium nigrescens Viv.(ball clover) as a strategy to improve the seed yield of white clover. Third generation backcross hybrids have now been developed in different leaf size categories that have the agronomic performance of white clover. Assessment of the seed yield of the hybrids in field experiments conducted over two harvest years showed that the medium and large leaved hybrids produced significantly more inflorescences and had a higher seed yield potential than control varieties of comparable leaf size improving the commercial potential of this material. Introgression of the rhizomatous trait from Caucasian clover (Trifolium ambiguum M. Bieb) into white clover has been used to improve persistence and tolerance of moisture stress. Advanced hybrids are now at the stage of development where they will be submitted to official variety trials.