When tetraploid wheat (Triticum durum Desf.) variety DR147 was crossed with maize (Zea mays L.) variety suppersweet ss 7700,
pollen readily germinated on the stigma and one or more pollen tubes reached the embryo sac in 83 4% of wheat florets. The frequency of fertilization and embryo formation was 44 5% and 42 6% respectively. The hybrids were karyotypically unstable and the maize chromosomes were eliminated early in the development. Thus
haploid wheat embryos were form. Although the double fertilization frequency of durum wheat×maize was high (32 7%) to form embryos and endosperms, yet the endosperms were highly abnormal. It was very difficult to produce viable mature seeds from the mother durum wheat plants. The survival of hybrid embryos produced by durum wheat×maize could be improved or prolonged by treatment with 100 ppm 2,4 D (either by dipping inflorescences in solution or injecting 0 3 to 0 5 mL 2,4 D solution into the uppermost internodes of the wheat stem). 9 to 13 days after pollination, caryopsis were excised from the pollinated spikes and surface sterilized for peeling of the embryos in different developing stages. The embryos were plated on MS solid medium containing 3% sucrose, 200 mg/L casein hydrolysate for embryo rescue. The experimental results revealed that the well developed embryos (larger than 0 5 mm with scutellum structure) were easy to produce calli by callus induction or produce haploid wheat plants by embryo rescue, whereas the
poorly developed embryos (globular, pear or torpedo shaped embryos smaller than 0 3 mm) responsed very poorly. The germination frequencies of well and poorly developed embryos were 83 3% and 12 5%, respectively. Chromosome counts of root tip cells of the rescued plants proved their haploid nature (2n=2x=14).