Development of a breeding strategy for interspecific hybrids between Caucasian clover and white clover

A single 8x F-1 hybrid between Caucasian clover (T ambiguum) and white clover (T repens) was backcrossed to seven white clover plants to generate fertile 6x BC1 families. To determine the most useful combination of desired traits of both parental species, and to develop a breeding strategy for this population, subsequent generations were produced in various ways. Self-pollination and intercrossing among BC1F1 families produced F-2 and later, F-3 and F-4 generations. Second, third and fourth backcrosses to white clover produced BC2 BC3 and BC4 generations. All generations were compared with the parental species in a single experiment grown in sand. Expression of the desired belowground traits of Caucasian clover was best in the BC, generation. By contrast, the best expression of the desired above-ground white clover traits was shown by the BC2F1 generation. However, the BC2F1 was pentaploid and did not stably transmit its desirable features to subsequent generations. On the other hand, advancement in the BC1 from F-1 to F-4 revealed significant positive variation in most of the important traits and suggested that selection would be successful. A breeding strategy was developed based on the genetically stable BC1 generation, advancing to BC1F6 by selecting for increases in shoot dry matter (DM), stolon numbers, stolon growth, improved nodal rooting radius, larger numbers of flowers and high fertility and seed-set.