DIFFERENTIATION OF PHYSIOLOGIC RACES OF URO-

Two physiologic races of the bean rust organism (Uromyces phaseoli typica Arthur), one collected in southern California and the other in the vicinity of Washington, D. C, were differentiated in 1935 by Harter, Andrus, and Zaumeyer (5).^ The one from California was designated form 1, and the one from the East, form 2. More recently Dundas and Scott (1), Parris,^ Harter (2), and others have recognized the existence of additional physiologic races and have utilized this information in the production of bean varieties {Phaseolus vulgaris L.) resistant to rust. Since the discovery of forms 1 and 2, the existence of many physiologic races has been proved from bean rust material collected from various parts of the country. The different races described in this paper were differentiated on the basis of their parasitic action on seven varieties of beans used as differential hosts. (See table 1.)