Virulence and Polymorphic DNA Relationships of<i>Puccinia striiformis</i>f. sp.<i>hordei</i>to Other Rusts

The relationships of Puccinia striiformis f. sp. hordei (stripe rust of barley) to P. striiformis f. sp. tritici (stripe rust of wheat) and P. striiformis f. sp. poae (stripe rust of bluegrass) in North America were determined by virulence and random amplified polymorphic DNA (RAPD) analyses. Their relationships to P. hordei (leaf rust of barley), P. recondita f. sp. tritici (leaf rust of wheat), and P. graminis f. sp. tritici (stem rust of wheat) were determined by RAPD assay. All isolates of P. striiformis f. sp. hordei were virulent on some cultivars of wheat, and some isolates of P.striiformis f. sp. tritici were virulent on some cultivars of barley. Isolates of P. striiformis f. sp. hordei and P. striiformis f. sp. tritici did not infect bluegrass, and isolates of P. striiformis f. sp. poae did not infect barley and wheat cultivars. Of 31 barley genotypes tested, 9 were susceptible and 8 were resistant to all isolates of P. striiformis f. sp. hordei. The remaining 14 genotypes showed differential reactions. Fourteen races (pathotypes) of P. striiformis f. sp. hordei were identified using eleven selected barley genotypes based on avirulence/virulence patterns. A system for naming and designating races of P. striiformis f. sp. hordei was presented to distinguish races of P.striiformis f. sp. hordei from races of P. striiformis f. sp. tritici. RAPD analyses separated the isolates of P. striiformis f. sp. hordei, P. striiformis f. sp. tritici, and P. striiformis f. sp. poae. P. striiformis f. sp. hordei and P. striiformis f. sp. tritici were more closely related to each other than they were to P. striiformis f. sp. poae. Based on molecular variation, none of the three formae speciales of P. striiformis were more closely related to P. hordei, P. recondita f. sp. tritici, or P. graminis f. sp. tritici.

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