In situ localization and morphology of the bacterium associated with ratoon stunting disease of sugarcane

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Abstract
Freshly sectioned tissues of sugarcane with ratoon stunting disease (RSD) were examined with the scanning electron microscope. The RSD-associated bacterium was recognized by its diameter, pleomorphism and xylem association. It commonly occupied the protoxylem and metaxylem vessels. The bacterium was observed in the gaps between secondary wall thickenings of xylem vessels and also adhering to the secondary wall. The lacunae, tracheids and xylem parenchyma cells also were invaded by the bacterium. The lumen of some infected xylem elements was filled with a dense network of bacterial cells. Remnants of a supporting matrix were observed in some of these lumina. Unicellular forms were most frequently observed; however, swollen forms, filamentous branching forms and microcolonies consisting of tightly aggregated bacterial cells previously described from extracts of diseased tissue were also observed.