Common Bacterial Blight of Beans

X. axonopodis pv. phaseoli is a non-spore-forming, Gram-negative aerobic bacterium. It is rod-shaped with a single polar flagellum. Colonies are yellow, convex and slimy on glucose-containing media. The slimy appearance is due to the production of an extracellular polysaccharide, xanthan gum, on media containing glucose. The fuscans variety can be distinguished by the production of a dark-brown diffusible pigment in media containing tyrosine and certain other media. The non-fuscous strains can also produce low levels of diffusible brown pigments if high levels of tyrosine are added to the culture media.