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.
New sources of resistance to Puccinia graminis Pers. f. sp. tritici Erikss. and Henn. in barley(Hordeum vulgare L.) should be identified and incorporated into breeding programs to ensure the continued resistance of barley to this pathogen. The objective of this study was to identify resistance to stem rust in barley accessions from the USDA Wiebe collection and determine the relationship of this resistance to resistance conferred by the T gene. Four accessions, PI 382313, PI 382474, PI 382915, and PI 382976, were selected as having good field resistance at the Winnipeg Agriculture Canada Research Station, Glenlea rust nursery in 1986. The field resistance of these four accessions was reconfirmed in the 1987 rust nursery and was found to be as effective as, or more effective than, that conferred by T. Seedling and adult plant tests were conducted in controlled environments with six races (C5, C10,C 17,C 25,C 35, and C53). In seedling tests, PI 382313 was resistant or moderately resistant to all six races. Both PI 382474 and PI 382915 were moderately susceptible to C35 and susceptible to the other five races. The PI 382976 was moderately resistant to C35 and C53, and moderately susceptible or susceptible to the other races. In adult plant tests, PI 382474 was resistant to C35 and PI 382313 was resistant to C17. Both PI 382915 and PI 382979 displayed little resistance as adults to the six races. Genetics studies with PI 382313 indicated that the field resistance of this accession was conferred by a single dominant gene that was different from T.
The inheritance of resistance to Puccinia coronata, awn development, lemma pubescence, and lemma color were studied in the Avena sterilis accessions CAV 4248, CAV 4656, and CAV 4904. Three independent, partially dominant genes (Pc-64, Pc-65, Pc-66) in CAV 4248, one partially dominant gene (Pc-67) in CAV 4656, and a dominant gene (Pc-68) in CAV 4904 were identified which conferred resistance to P. coronata. Genes Pc-64, Pc-65, Pc-66, Pc-67, and Pc-68 conferred resistance to 13, 8, 6, 12, and 14 races, respectively, of the 14 races of P. coronata tested. Gene Pc-68 conferred resistance to all field isolates of P. coronata collected in Canada in 1981 and was found to be closely linked or allelic to gene Pc-46. Awns and lemma pubescence were inherited monogenically in crosses with all three CAV accessions. Grey lemma color was controlled by one gene in CAV 4248 and by two genes in CAV 4656. Brown lemma color was controlled by one gene, which was closely linked or pleiotropic with the gene for lemma pubescence in CAV 4904. There was no association between crown rust resistance and the three floret characters studied.
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