S. 2015. Agrobacterium-mediated genetic transformation of peanut and the efficient recovery of transgenic plants. Can. J. Plant Sci. 95: 735Á744. Four genotypes of peanut and two sources of explants (cotyledon and mesocotyl) were tested for their susceptibility to genetic transformation by the Agrobacterium tumefaciens strain LBA4404 that harbored the binary vector pCAMBIA1301. This plasmid contains the hygromycin phosphotransferase (hpt) and b-glucuronidase (GUS) genes, each under the control of a CaMV35S promoter. Comparative analyses of regeneration and transformation efficiencies indicated that mesocotyl was a better target tissue than cotyledon, and peanut genotypes of that mature early and have relatively small seeds (such as Huayu 26 and Huayu 20) were shown to be comparatively responsive to transformation. Sonication of explants soaked with solutions containing Agrobacterium was shown to optimize transformation. Culture of explants on medium supplemented with 3 mg L(1 indole-3-butyric acid and 0.1 mg L (1 napthaleneacetic acid enabled vigorous rooting from almost all transgenic shoots. More than 85% of the transplanted plants could produce morphologically normal flowers and pods with viable seeds. Phenotypic and genotypic monitoring of the inheritance of hpt and GUS genes through two generations indicated the expected 3:1 inheritance. Our results make Agrobacterium-mediated transformation a viable and useful tool for both breeding and functional genomic analysis of peanut.