Embryo rescue and induction of somatic embryogenesis as a method to overcome seed inviability in Zea mays ssp mays x Zea mays ssp parviglumis crosses

Zea mays ssp. mays (2n=40) and Z. mays ssp. parviglumis (2n=20) were crosse d to obtain hybrid plants by embryo rescue. Hybrid embryos were isolated an d cultured on Garcia et al. (1992) basic medium supplemented with 2,4-dichl orophenoxyacetic acid and/or kinetin in different concentrations. Caryopses harvested 23 d after pollination (DAP) were turgid, with 0.3 to 0.5 mm lon g embryos, while those harvested 30 DAP were shrunken, with 1 to 1.5 mm lon g embryos. Twenty days after plating, 100 % of the younger embryos gave ris e to white, compact embryogenic calli. Subsequently, coleoptiles, leaf-like structures, shoots and roots originated from them and 35 hybrid plants wer e regenerated from 60 embryos. Embryogenic or organogenic calli frequencies did not differ among hormonal treatments, but they decreased, on average, from 90.5 to 44.3 %, comparing 50 and 120-d-old cultures. The older embryos regenerated plants only by germination, although they gave rise to organog enic callus with low frequencies. Regenerated plants showed a somatic chrom osome number of 2n=30, pollen fertility of 40 to 80 % and 15 % viable naked caryopses.