Isolation, culture and ultrastructure of a xylem-limited bacterium associated with Sumatra disease of cloves

A xylem-limited bacterium (XLB) previously shown to be associated with Sumatra disease of clove trees was consistently isolated from diseased but not from healthy trees. Isolation of the XLB was most successful using freshly expressed bacterial ooze obtained from root and branch tissues with low to moderate levels of xylem vessel invasion in trees at early stages of disease. XLB were commonly isolated from trees with the rapid form of disease but infrequently from those with slow decline. Bacterial colonies grew slowly on nutrient agar, reaching a maximum diameter of 1 mm in 5-7 days at 28^oC. Cells of the bacterium were 0.5-0.6 μm in width and 1.0-1.5 μm in length and did not possess flagella. The bacterial envelope was strongly rippled and Gram negative.