Parasitic and pathogenic variation of soybean rust fungi and their geographic distribution.

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Morphological and host-range studies showed that six Phakopsora species, five Cerotelium species, and three Milesia species are recognized as the pathogen of rust diseases of legumes in the world. Among these, two Phakopsora species were previously unknown.Detailed comparative studies in telial morphology, parasitic ability(as shown by a host range), and pathogenic ability to soybeans and other cultivated legumes resulted in the recognition of two phakopsoroid fungi that incite soybean rusts in Asia and Neotropics. The Asian fungus is Phakopsora pachyrhizi H. Sydow & P. Sydow. This fungus is strongly pathogenic to soybeans but not to common beans, and its principal hosts under field conditions are Glycine max, Fachyrhizus erosus, Vigna unguiculata, Glycine soia, , Pueraria lobata, and Pueraria sontana. On the other hand, the Neotropic fungus is Phakopsora meibomiae(Arthur)Arthur and weakly pathogenic to soybeans and strongly pathogenic to common beans. Its principal hosts are Lablab purpureus, Phadeolus coccineus, Phaseolus lunatus, Phaseolus vulgaris, Aeschinomene americana, Canavalia villosa, Crotalaria spp., and Desmodium spp.Previously published inoculation experiments have revealed the existence of several host plants(all cultivated)common to both Asian and Neotropic fungi and many other potential hosts common to both fungi.