Reproductive characters of interspecific hybrids between Trifolium repens L. and T. nigrescens Viv.

The amphidiploid Trifolium repens L. (2n = 4x = 32) is one of the most agronomically important of the 250-300 species in the genus Trifolium. Seed production is, however, variable and often poor, because of a number of interacting reproductive and climatic factors. Improvement to those characters influencing seed production may be achieved by interspecific hybridization using a closely related species within the genus. One species which has been demonstrated to have a close affinity with T. repens is the annual T. nigrescens (2n = 2x= 16), a prolific flower producer with a less intermittent pattern of flowering than T. repens. Specific cross-combinations of T. repens and 7. nigrescens readily produced hybrids without the need of embryo culture. Some F, hybrids produced large numbers of seed when backcrossed to T. repens. Chromosome counts, isoenzymes and leaf markers confirmed that these were true hybrids. The F, s and BQs were vigorous plants demonstrating intermediate reproductive characters inherited from the two parental species. This novel approach may be a means of extending the range of heritable variation useful in the breeding and selection of T. repens.