Comparing mating designs to restore seed production of interspecific hybrids between Trifolium repens (white clover) and Trifolium uniflorum

Interspecific hybrids between Trifolium uniflorum and cultivated white clover (T. repens) have highly useful characteristics for temperate pastoral systems derived from the donor species. However, the early hybrids (F1 and BC1) also have unacceptably poor seed production for commerce. This study analysed the basis for the poor seed production and investigated breeding strategies for overcoming the problem. The BC1F1 generation produced lower than expected numbers of heads per plant and seeds per floret. Backcrossing of selected hybrids to white clover as expected recovered the target seed production phenotype and created new variation. Significantly, however, seed numbers also returned to near target levels by recurrent selection within the BC1 generation. Thus it was possible to retain a theoretical average of 25% of T. uniflorum genome and still achieve high seed production per plant. Both BC1F2 and BC2F1 generations produced high seed numbers per plant, along with reasonable variation. Thus both second generation hybrid forms have high reproductive potential and should be the focus for the selection of the desired combinations of agronomic and seed production traits.