Interspecific hybridization of red clover (Trifolium pratense L.) with T. sarosiense Hazsl. Using in vitro embryo rescue.

Interspecific hybrid clover plants from the cross Trifolium sarosiense Hazsl. X T. pratense L. were obtained in the present investigation. Immature hybrid embryos were excised aseptically from the pistillate parent, T. sarosiense (2 n = 48), and cultured in vitro prior to in situ abortion. Agar-solidified nutrient media modified from that developed previously for tissue and cell cultures of red clover (2 n = 14) were used for embryo rescue.The heart shaped embryos obtained were cultured for 8 to 14 days on a medium containing a high level of sucrose, a moderate level of auxin, and low cytokinin activity. Viable embryos were then transferred to a standard medium with low auxin and moderate cytokinin levels for the direct germination of shoots. Some embryos produced only callus. Plants were regenerated from callus using an alternate culture scheme. Hybrid shoot numbers were increased on a low auxin, high cytokinin medium and subsequently rooted before transfer to soil in the greenhouse.About 10% of the hybrid embryos were rescued using the optimal culture sequence. Five full-sib families of the F1 hybrid were successfully grown to maturity. Root-tip cells of hybrid plants possessed the expected somatic chromosome number of 31. The genetically determined leaf-mark trait carried by the staminate parent and the rhizomatous root habit of the pistillate parent were expressed in hybrid plants.