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Genetic analysis of broad-spectrum resistance in Mesoamerican common bean accession PI 310762 to the hypervariable bean rust pathogen.
M. PASTOR-CORRALES (1). (1) USDA-ARS, Beltsville, MD, U.S.A.

The devastating rust disease of common bean (<i>Phaseolus vulgaris</i>) is caused by <i>Uromyces appendiculatus</i>, a pathogen known for its extensive virulence diversity. Hundreds of races of this pathogen have been identified throughout the world. The Mesoamerican bean PI 310762 has remarkable broad-spectrum rust resistance to 89 of 90 races from different parts of the world and which are maintained at Beltsville, Maryland. Moreover, PI 310762 is resistant to races that render susceptible all ten named and mapped rust resistance genes known in common bean. These races also infect other common bean cultivars with broad-rust resistance but with unnamed and unmapped genes. To determine the inheritance of rust resistance in PI 310762, it was crossed with Pinto 114, a common bean cultivar that is susceptible to 88 of the 90 races maintained at Beltsville. Seedlings of the parents, F<sub>1</sub>, F<sub>2</sub>, and BC<sub>1</sub> populations, were inoculated with two Mesoamerican and two Andean races under controlled greenhouse conditions. The resistant reaction of PI 310776 to all races used in this study was expressed as minute uredinia, smaller than 0.3 mm in diameter. The susceptible reaction of Pinto 114 was expressed as large uredinia, larger than 0.5 mm in diameter. Genetic analysis of the rust resistance based on the infection type observed on 157 plants of the F<sub>2</sub> population fit a 3:1 resistant-susceptible ratio, suggesting that resistance in PI 310761 to <i>U. appendiculatus</i> is conferred by a single and dominant gene. <p><p>Keywords: Fungus, Legumes, Beans

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