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A new set of international differential hosts for characterizing the virulence of cultures of Puccinia graminis f. sp. tritici including the host resistance genes Sr5, 6, 7b, 8a, 9b, 9e, 99, I I, I 7, 2 l, 30, and 36 is proposed. Additionally, a resistant series that consists ofhost genes 5r13,22,24,25, 26,2'7. 31,32, 33, and 37 that have generally been resistant worldwide is recommended for evaluating bulk collections or composites of individual cultures. The use ofadditional differential hosts oflocal interest, especially those related to national breeding programs, is encouraged. Races are to be designated by a three-letter code (Pgt-code) followed by a hyphen and a listing of those host genes in the 'resistant' set on which the race was virulent. Data on local supplemental series should be separated from the Pgt-code by a slash. A central type-culture collection is proposed and will be maintained at the Cereal Rust Laboratory at St. Paul, MN, for use in breeding and research programs. Type-cultures will be evaluated against the resistance conferred by the known single genes.

No abstract