Production of an Interspecific Triploid Hybrid Between Gossypium hirsutum and G. Arboreum by Embryo Rescue

Hand pollination of G. hirsutum (2n= 4x= 52, AA D1D1) with G. arboreum (2n= 2x= 26, A1A1) produced 18.7% hybrid seeds. None of the hybrid seeds germinated in pots and in all likelihood the embryo (A1AD1) and the endosperm (A1AAD1D1) were incompatible. In vitro culture of ovules 5 days after pollination (DAP), failed to support the growth of viable embryos. Hybrid embryos 50 DAP, excised from field pollinated hybrid seeds, successfully germinated in vitro. Triploid hybrid plants were successfully grown to flowering in pots. The frequency of generation of hybrid plants was 2.3% of cultured embryos. Pollen mother cells of the hybrid plant showed the expected A genome ring of 4 and ring of 6 chromosomes. In addition, there were several unpaired chromosomes of the D genome at metaphase I. The unpaired chromosomes grouped randomly at MII and organized spindles around them. The mature pollen grains were sterile due to aneuploidy.