Xanthomonas fuscans subsp. fuscans — a Pathogen of Small Brown Spot of Legumes

Xanthomonas fuscans subsp. fuscans is known as an obligate phytopathogen — the pathogen of small brown spot of beans that gradually expands the range of host plants and spreads worldwide on legumes. The review provides data on the problems of the pathogen’s systematics and its change depending on the new research and improvement of methods for studying biological properties. Historical data on the first stages of isolation of X. fuscans subsp. fuscans from bean and new stages of its spread and isolation from soybean in Ukraine, after which the pathogen moved from the monophage to polyphage status within the same plant family. The importance of X. fuscans subsp. fuscans as a potentially dangerous phytopathogen, as evidenced by the presence of its samples in many collections of living microorganisms in the world and the quarantine status of the pathogen in a number of European countries are underlined. It has been shown that the phytopathogen X. fuscans subsp. fuscans does not differ significantly from other xanthomonads in terms of its cultural, morphological, physiological, and biochemical properties, especially those that cause diseases of leguminous plants. At the same time, the only but the main feature of this bacterial culture is emphasized — the increased amount and activity of the intracellular enzyme tyrosinase, which distinguishes X. fuscans from all other bacterial phytopathogens and not only among xanthomonads. The variants of the stage of synthesis of tyrosinase and melanin in bacteria, due to which the black-brown pigment is formed, and the lack of research on the pathway of tyrosinase synthesis in phytopathogenic bacteria, in particular X. fuscans subsp. fuscans, are analized. The data on genotypic properties of X. fuscans subsp. fuscans, its affinity with other pathogens of the genus Xanthomonas that cause diseases of leguminous plants, and the possible role of the phenomenon of «horizontal gene transfer» in their affinity along with differences in biological properties are considered. The analyzed literature indicates the potential danger of the causative agent of small brown spot of legumes and the need for constant monitoring of the spread and study of its biological properties to develop methods for controling the spread of X. fuscans subsp. fuscans.