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Bulked Segregant Analysis Identifies Molecular Markers Linked to Melampsora medusae Resistance in Populus deltoides

First and fifth authors: Departments of Forestry and Plant Pathology, Iowa State University, Ames 50011; second author: USDA Forest Service, Southern Research Station, Southern Institute of Forest Genetics, 23332 Highway 67, Saucier, MS 39574; third author: USDA Forest Service, Rocky Mountain Research Station, Forestry Sciences Laboratory, 1221 South Main, Moscow, ID 83843; and fourth author: Department of Forestry, Iowa State University, Ames 50011

In the north central United States, leaf rust caused by Melampsora medusae is a major disease problem on Populus deltoides. In this study we identified molecular markers linked to a M. medusae resistance locus (Lrd1) that was segregating 1:1 within an intraspecific P. deltoides family (C9425DD). Previous field results were confirmed in the controlled environment of a growth chamber through an excised whole-leaf inoculation method. Using bulked segregant analysis we identified two random amplified polymorphic DNA (RAPD) markers (OPG10₃₄₀ and OPZ19₁₈₀₀) that are linked to Lrd1. Based on segregation in a total of 116 progeny, the genetic distances between OPG10₃₄₀ and OPZ19₁₈₀₀ and the resistance locus were estimated as 2.6 and 7.4 Haldane centimorgans (cM), respectively. Multipoint linkage analyses strongly suggest the most likely order for these loci is Lrd1, OPG10₃₄₀, and OPZ19₁₈₀₀. These markers may prove to be instrumental in the eventual cloning of Lrd1, as well as for marker-assisted selection of leaf-rust resistant genotypes.

Additional keywords: intraspecific hybrids, polymerase chain reaction, resistance genes.