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Isolation and Characterization of Opine-Utilizing Strains of Agrobacterium tumefaciens and Fluorescent Strains of Pseudomonas spp. from Rootstocks of Malus. M. L. Canfield, Senior research assistant, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331-2902; L. W. Moore, professor, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331-2902. Phytopathology 81:440-443. Accepted for publication 9 November 1990. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/Phyto-81-440.

Media containing opines were used to isolate Agrobacterium tumefaciens and fluorescent Pseudomonas spp. from rootstock tumors and roots of Malus. Strain B49C of A. tumefaciens was used to inoculate cultivars Mark, EMLA 7, and Red Delicious seedling apple rootstocks in field trials at two nurseries in Washington state. Crown gall incidence was greater on inoculated than on uninoculated controls at both locations. Of 12 strains of A. tumefaciens isolated, three utilized mannopine, four utilized nopaline, and four utilized both mannopine and nopaline as the sole carbon and nitrogen source in culture media. None of the 12 strains utilized octopine, and one utilized none of the three opines tested. Forty-one strains of Pseudomonas spp. utilized octopine, 48 utilized nopaline, one utilized both octopine and nopaline, and none utilized mannopine. Seventy-seven of the isolates of Pseudomonas spp. inhibited the growth of A. tumefaciens in culture.