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Microcolonies of the Bacterium Associated with Ratoon Stunting Disease Found in Sugarcane Xylem Matrix. J. Kao, Graduate Assistant, Department of Plant Pathology, Louisiana State University, Baton Rouge, LA 70803; K. E. Damann, Jr., Assistant Professor, Department of Plant Pathology, Louisiana State University, Baton Rouge, LA 70803. Phytopathology 68:545-551. Accepted for publication 20 October 1977. Copyright 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-545.

Microcolonies of a filamentous, branched organism were observed by phase-contrast and interference-contrast microscopy in vascular extracts from internodes of sugarcane with ratoon stunting disease. The microcolonies were present in a matrix extracted from the xylem vessels of internodes by negative pressure. Matrices and microcolonies were not found in sugarcane known to be free of the disease. Electron microscopy revealed branched chains of cells with septa and mesosomes. The individual cells of the filaments were characteristic of the previously described coryneform bacterium associated with the disease. Vascular extracts from one- or two-node cuttings of diseased cane did not reveal matrices or microcolonies but did contain the individual cells or short branched chains of the organism. The filamentous spiderlike morphology of the microcolonies and true branching suggest a relation to the Actinomycetales.