RESEARCH ARTICLE A New Synthetic Amphiploid (AADDAA) between Gossypium hirsutum and G. arboreum Lays the Foundation for Transferring Resistances to Verticillium and Drought

Gossypium arboreum, a cultivated cotton species (2n = 26, AA) native to Asia, possesses invaluable characteristics unavailable in the tetraploid cultivated cotton gene pool, such as resistance to pests and diseases and tolerance to abiotic stresses. However, it is quite diffi-cult to transfer favorable traits into Upland cotton through conventional methods due to the cross-incompatibility ofG. hirsutum (2n = 52, AADD) andG. arboreum. Here, we improved an embryo rescue technique to overcome the cross-incompatibility between these two pa-rents for transferring favorable genes fromG. arboreum intoG. hirsutum. Our results indi-cate that MSB2K supplemented with 0.5 mgl-1 kinetin and 250 mg-1 casein hydrolysate is an efficient initial medium for rescuing early (3 d after pollination) hybrid embryos. Eight pu-tative hybrids were successfully obtained, which were further verified and characterized by cytology, molecular markers and morphological analysis. The putative hybrids were subse-quently treated with different concentrations of colchicine solution to double their chromo-somes. The results demonstrate that four putative hybrid plants were successfully chromosome-doubled by treatment with 0.1 % colchicine for 24 h and become amphiploid