Author
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Stavely, J |
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Submitted to: Bean Improvement Cooperative Annual Report
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 5/5/1998 Publication Date: N/A Citation: N/A Interpretive Summary: The rust disease of edible, common beans is a major economic problem for producers and ultimately consumers. It is most efficiently controlled by cultivar resistance. The fungus causing bean rust is highly variable so the most broadly effective resistance genes need to be combined to protect against new pathogenic races. Two such major genes for rust resistance were previously thought to be alternatively, one or the other at the same location (allelic) so that both could not be stably incorporated together into bean cultivars. They were designated Ur-3 and Ur-3-2. Genetic studies demonstrate that these two genes are closely adjacent (linked) to each other in such a way that when one is present in its effective (dominant) condition the other is in its ineffective (recessive) condition. This is termed linkage in repulsion. So the Ur-32 gene is redesignated as Ur-11. After several generations of large populations of plants from crosses between plants with one or the other dominant gene, the linkage has been broken to produce plants with both dominant genes, resistance to all races of the fungus, and both genes for resistance to many important races. The Ur-3 and Ur-11 genes are independent of three other major genes so all five can now be combined into cultivars. Multiple gene resistance will better protect against new races of the fungus, improve production efficiency, market stability, dependability of food supplies, and reduce pesticide usage. Technical Abstract: Due to previous lack of success in obtaining bean (Phaseolus vulgaris L.) breeding lines homozygous for two major rust (Uromyces appendiculatus (Pers.) Unger var. appendiculatus) resistance genes, these genes were presumed to be allelic. One of these genes had been named Ur-3 and the other was tentatively named Ur-3-2. Discovery of the first among 87 identified races of the rust fungus against which Ur-3-2 was not effective, but against which Ur-3 was effective led to evaluation of progeny populations from crosses between plants having homozygous Ur-3 and no Ur-3-2 with plants having homozygous Ur-3-2, but no Ur-3. Segregation in the F-2, confirmed in subsequent generations, indicated that Ur-3 and Ur-3-2 are at different, but closely linked loci and are linked in repulsion. So Ur-3-2 has been renamed Ur-11. This linkage has been broken to produce F-4 populations that contain both dominant alleles. Other major dominant rust resistance genes Ur-4, Ur-5, and Ur-6 are independent of Ur-3 and Ur-11. |
