Tissue culture increases meiotic pairing of regenerants for barley x Canada wild rye hybrids

Canada wild rye (CWR; Elymus canadensis L.) expresses traits such as barley yellow dwarf virus resistance, winter hardiness, and drought resistance. Hybrids between CWR and barley (Hordeum vulgare L.) are sterile, precluding transfer of these traits into barley. Callus cultures were initiated from these hybrids to promote chromosome recombination and possibly restore fertility. The objectives of this study were to determine the effects of tissue culture and cytoplasms on meiotic pairing of 17 intergeneric hybrids generated by crossing Betzes barley and CWR, and 117 regenerants, and to examine meiosis in a BC1 plant from a regenerant x barley cross. Meiotic abnormalities were common, including chromosome bridges, lagging univalents, and micronuclei. Regenerants with 2n = 21, 20, or 22 chromosomes had significantly greater pairing and fewer micronuclei than the hybrids (2n = 21). Regenerants with partially or completely doubled chromosome complements (2n = 36-42) showed chromosome instability. Hybrids and regenerants with barley cytoplasm had significantly more pairing and fewer micronuclei than those with CWR cytoplasm. Application of barley pollen to florets of a stably doubled (2n = 42) regenerant resulted in a single BC1 plant that survived to develop spikes. This plant had the expected 28 mitotic chromosomes and showed meiotic chromosome number instability. Backcrosses to this plant produced small embryos for rescue, indicating that the BC1 plant is partially female fertile. Attempts to recover BC2 plants are in progress. Results indicate that tissue culture significantly increased chromosome pairing, providing additional opportunity for genetic recombination between the two species.