Studies of physiologic specialization in the fungus causing leaf rust of Wlleflt, Pttccinia retJondita Rob.ex Desm.f. sp.tritici, were sLarted by :Mains and Jackson (7)3 at Purdue University in 1918.They estab lished a set of 11 differential varieties of wheat and described 12 physiologic races of the fungus.Three varieties were soon discarded and the remaining eight (6) became known as the International Standard differentIal varieties.These varieties have been used in many countries as a basis for race identification.The races reported ha.ve been recorded in an International Register of Physiologic Races of the fungus through several revisions (4-,5)4 coordinated by the late senior author of tl1is bulletin.Beginning in 1926, collections of P. ?'econdita f. sp.tritici in wheat growing areas of the United Stat•cs wcre analyzed for their physiologic mce content each year.Summaries of results were published each year from 1951 through 1960, but no long-term summary has been made.This bulletin summarizes elata, obtll.ineelfrom 1926 through 1960.
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Johnston et al. (1968) studied this question.