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

Abstract

A single 8× F1 hybrid between Caucasian clover (T. ambiguum) and white clover (T. repens) was backcrossed to seven white clover plants to generate fertile 6× 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 F2, and later, F3 and F4 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 below‐ground traits of Caucasian clover was best in the BC1 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 F1 to F4 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.