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Characterization of an Unusual New Agrobacterium tumefaciens Strain from Chrysanthemum morifolium Ra

Characterization of an Unusual New Agrobacterium tumefaciens Strain from Chrysanthemum morifolium Ra

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Vol. 57, No. 9 APPLIED AND ENVIRONMENTAL MICROBIOLOGY, Sept. 1991, p. 2468-2472 0099-2240/91/092468-05$02.00/0 Copyright © 1991, American Society for Microbiology Characterization of an Unusual New Agrobacterium tumefaciens Strain from Chrysanthemum morifolium Ramt ARLA L. BUSHt* AND STEVEN G. PUEPPKE Department of Plant Pathology, University of Missouri, Columbia, Missouri 65211 Received 26 March 1991/Accepted 20 June 1991 We characterized five isolates of Agrobacterium tumefaciens from naturally occurring galls on Chrysanthe- mum morifolium. The isolates are similar, possibly identical, members of a single strain of A. tumefaciens that we designate Chry5. The strain is a biotype I, as indicated by its response to both newly described and traditional biotype tests. Chry5 produces tumors on at least 10 plant species. It is unusual in its ability to form efficiently large tumors on soybean (Glycine max), a species normally refractory to transformation. Chry5 is unable to utilize octopine or mannopine as a carbon source. Although Chry5 can catabolize a single isomer each of nopaline and succinamopine, it differs from other known nopaline and succinamopine strains in its insensitivity to agrocin 84. This pattern of opine catabolism is unique among Agrobacterium strains examined to date. All five isolates of Chry5 contain at least two plasmids, one of which shares homology with pTiB6. Crown gall, a disease that affects a wide variety of plant species (11), is caused by the bacterial pathogen Agrobacte- rium tumefaciens. The disease attracts considerable atten- tion because of the ability of the causal organism to act as a natural genetic engineer. A piece of bacterial DNA, the T-DNA, is transferred into a plant cell, where it is integrated into the genome and expressed, giving rise to the gall (see references 36 and 43 for reviews). Strains of A. tumefaciens are diverse and have been classified in several ways. Three biotypes have been recog- nized (18, 29) on the basis of pattern of responses to a variety of biochemical and physiological tests. A. tumefaciens strains also can be subdivided according to their abilities to catabolize opines or to produce them in tumors (13, 32); these characteristics are specified by the Ti plasmid (5, 24). Although early work dealt only with octopine and nopaline, increasing numbers of tumor-specific compounds are being described (33). Alternatively, strains have been categorized by various aspects of host range. For example, an A. tumefaciens strain can be described as having wide or limited host range on the basis of the number of susceptible plant species. Host range appears to be an isolate-specific characteristic, since dif- ferent isolates from a single tumor can show distinctive patterns of specificity (1). The ability of a strain to cause tumors on different subspecies, or cultivars, of a single host also may vary. This has been observed in a variety of plants (for some examples, see reference 14 and references there- in). In all instances, some degree of specificity is apparent, indicating that even closely related plants can differ in susceptibility.
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