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Two dimensional electrophoretograms of detergent-soluble polypeptides extracted from dormant urediospores were used to compare inter-and intraspecific relationships among nine races of rye stem rust (Puccinia graminis f. sp. secalis) , a hybrid between rye stem rust and wheat stem rust (P. graminis f. sp. tritici), and its parents. More than 280 polypeptides were detected in each race of rye stem rust. The nine races differed by one to five genes for virulence and by five to seven polypeptides, but these differences were not correlated. The rye/wheat stem rust hybrid, rye stem rust parent and wheat stem rust parent differed by 12 polypeptides. The polypeptide patterns of the rye stem rust races were similar to those previously found for wheat and oat stem rusts. Rye stem rust and wheat stem rust had 270 polypeptides in common, and differed by 17 polypeptides. In contrast, ninety-two polypeptides separated rye and oat stem rusts. The considerable homology in polypeptide patterns is consistent with the view that these three cereal stem rusts are related, and that rye stem rust and wheat stem rust have the closest genetic relationship.
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