ARS | Publication request: High-resolution mapping of the wheat Lr46 pleiotropic rust resistance locus

Submitted to: Abstracts of International Powdery Mildew Conference
Publication Type: Abstract Only
Publication Acceptance Date: August 5, 2009
Publication Date: N/A

Technical Abstract: Rust diseases are the most important diseases of wheat globally, and genetic resistance is the most effective method for controlling all three rusts. Numerous resistance genes have been characterized and reported. For typical resistance genes, the mechanism of resistance and the basis of race specificity are due to gene-for-gene interactions between host resistance (R) gene products and pathogen avirulence (Avr) gene products. Durable rust resistance based on R genes remains elusive in wheat, but some resistance genes are thought to be durable because they are not dependent on the recognition of a single Avr gene product. The pleiotropic Lr46 gene confers durable, race non-specific resistance to leaf rust and stripe rust but little is known about it’s mechanism of action. Using a population of 3931 lines with a genetic resolution of approximately 0.01 cM, fine-scale mapping of the Lr46 locus was carried out for both the development of molecular markers and map-based cloning of the gene. Existing markers were used to probe wheat hexaploid and tetraploid bacterial artificial chromosome (BAC) libraries and, following low-pass sequencing of selected BACs, contigs were assembled that were the source of many additional markers. Because no recombination was detected between BAC-derived markers, synteny was explored with the model grass genome, Brachypodium distachyon. Markers spanning the Lr46 locus were colinear with a 90 kbp physical region from Brachypodium supercontig 2, which was used to identify wheat ESTs and develop new markers. Subsequently, we delimited Lr46 to a 20 kbp physical region of Brachypodium distachyon. The newly developed markers were evaluated on diverse germplasm lines to test there efficacy for marker-assisted selection for the Lr46 locus.