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A Fastidious, Xylem-Limited Bacterium Infecting Ragweed. L. W. Timmer, Associate professor, Agricultural Research and Education Center, University of Florida, Lake Alfred 33850; R. H. Brlansky(2), R. F. Lee(3), and B. C. Raju(4). (2)(3)Assistant professors, Agricultural Research and Education Center, University of Florida, Lake Alfred 33850; (4)Chief plant pathologist, Yoder Brothers, Inc., Box 68, Alva, FL 33920. Phytopathology 73:975-979. Accepted for publication 19 January 1983. Copyright 1983 The American Phytopathological Society. DOI: 10.1094/Phyto-73-975.

A fastidious, ragweed xylem-limited bacterium (RgXLB) was isolated that grew well on media developed for the phony peach (PP) bacterium, but not on media for the Pierce's disease (PD) bacterium. Xylem vessels of ragweed (Ambrosia artemesiifolia) mechanically inoculated with the RgXLB became heavily colonized. Infected ragweed was stunted compared to healthy controls, but showed no other symptoms. The disease was designated ragweed stunt. The RgXLB was transmitted from ragweed to ragweed by the sharpshooters. Oncometopia nigricans and Homalodisca coagulata. Plum became infected following mechanical and insect vector inoculations, periwinkle only following mechanical inoculations, and grape, peach, and citrus were not infected. The RgXLB was reisolated from infected plum and periwinkle, but the plants did not develop symptoms. Bacteria from ragweed and from culture were small and rod-shaped (0.3- 0.5 x 1.5- 3.0 μm) with a rippled cell wall typical of other xylem-limited bacteria (XLB). The cibaria and precibaria of O. nigricans were colonized by the RgXLB in a manner similar to that of other XLB. In enzyme-linked immunosorbent assay, the RgXLB reacted more strongly with antiserum to the plum leaf scald (PLS) bacterium than to antiserum to PD bacterium. In reciprocal tests, the PLS bacterium reacted more strongly with an antiserum prepared to the RgXLB than did the PD bacterium. The RgXLB appears to be closely related to, but pathologically distinct from, the PLS and PP bacteria and more distantly related to other XLB based on cultural characteristics, host range, and serological tests.

Additional keywords: ragweed stunt, rickettsialike bacteria.