Interspecific hybridization of Trifolium alexandrinum with T. constantinopolitanum using embryo rescue.

The embryo rescue technique was successfully used to raise hybrids between Trifolium alexandrinum and T. constantinopolitanum. As a result of its narrow genetic base, genetic improvement in Egyptian clover (syn. Berseem; T. alexandrinum), an important fodder crop in tropical and subtropical countries, is hampered, thereby making it imperative to introduce alien genes from related species. In a conventional interspecific hybridization program, hybrids could not be raised due to post-fertilization barriers. Of the several combinations tried, pollination 2 days after emasculation was found to be the best. Globular embryos were observed 5-7 days after pollination (DAP), followed by heart-shaped embryos 10-12 DAP. Embryos excised at the heart-shaped stage responded well to EC3 culture medium. Of 612 crosses, 33 healthy embryos could be excised and cultured on EC3 medium. The plumule emerged 8-12 days following inoculation. The embryo-rescued plants were hardened, inoculated with Rhizobium and transferred to the field. The hybrids showed intermediate morphological features with reduced pollen fertility (55-65%) and a chromosomal complement of 2n = 16. Biochemical characterization using isozymes confirmed hybridity.