MAP-BASED CLONING OF Mmd1, A POPLAR LEAF RUST RESISTANCE GENE

¹ University of Washington Center for Urban Horticulture, 3501 NE 41st St., Seattle, WA 98195 USA

² Washington State University, Puyallup Research Extension Center, 7612 Pioneer Way, E. Puyallup, WA 98371-4998 USA

Poplar leaf rust, caused by species of the fungal pathogen Melampsora, is one of the most important diseases of hybrid poplar in the world. Resistance to Melampsora medusae and Melampsora x columbiana 3, two rusts common to the Pacific Northwestern United States, is conferred by a single dominant locus, Mmd1. We are attempting to isolate the Mmd1 locus using a map-based cloning strategy. To provide a starting point for positional cloning, we developed a high-resolution genetic map around the Mmd1 locus that contains 6 AFLP markers and spans a map distance of 2 centiMorgans. All tightly linked markers were analyzed on an F1 population consisting of 2000 individuals that was established from an interspecific cross between a heterozygous resistant Populus trichocarpa female and a homozygous susceptible Populus deltoides male. Two very tightly linked markers, E53/M70_01 and E47/M48_01, mapped within 0.05cM (10-20kb) of the Mmd1 locus. One of these markers, E53/M70_01, has been cloned, sequenced, and developed as a sequenced-tagged-site marker (BVS1). We are currently using BVS1 to screen a bacterial artificial chromosome (BAC) library constructed from the resistant P. trichocarpa parent.