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Recombination Within a 5-centimorgan Region in Diploid Avena Reveals Multiple Specificities Conferring Resistance to Puccinia coronata. Roger P. Wise, Field Crops Research Unit, Agricultural Research Service, U.S. Department of Agriculture, Department of Plant Pathology, Iowa State University, Ames 50011; Michael Lee(2), and P. John Rayapati(3). (2)(3)Department of Agronomy, Iowa State University, Ames 50011. Phytopathology 86:340-346. Accepted for publication 21 December 1995. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1996. DOI: 10.1094/Phyto-86-340.

A set of 100 recombinant inbred lines (RILs) was produced from a cross of diploid (n = 7) Avena strigosa (CI 3815) with A. wiestii (CI 1994), resistant and susceptible, respectively, to Puccinia coronata, the causal agent of crown rust. This set of RILs was inoculated with 11 isolates of P. coronata. Infection type reactions to eight isolates (PC54, 263, 290, PC62, 202, 325A, PC58, and PC59) fit a 1:1 resistant/susceptible ratio expected for traits controlled by single genes. Reaction to isolate 264B fit a 3:1 resistant/susceptible ratio, suggesting resistance conditioned by two dominant genes. Reaction to isolate 276 fit a 1:3 resistant/susceptible ratio, suggesting control by two dominant genes, whereby one gene inhibits the resistance conferred by the other. All isolates detected resistance specificities that mapped to the Pca region in A. strigosa for resistance to P. coronata. Pca is positioned between the oat restriction fragment length polymorphism marker Xisu2192 and a new randomly amplified polymorphic DNA marker, XisuC18, near the end of linkage group A. Five unique specificities within the Pca region were differentiated by recombination. The observation of five specificities conferring disease resistance that are linked in coupling is unusual, because such genes generally are linked in repulsion and inherited from multiple donor parents.