TOWARDS CLONING THE GENE FOR RESISTANCE TO WHITE PINE BLISTER RUST

Institute of Forest Genetics, USDA Forest Service, Department of Environmental Horticulture, One Shields Avenue, University of California Davis, CA 95616 USA

White pine blister rust (WPBR) (causal agent Cronartium ribicola) is a fungal disease that has reached epidemic proportions and is predicted to have catastrophic ecological consequences. All North American white pines (genus Strobus) are susceptible. However, a small percentage of sugar pine (Pinus lambertiana), western white pine (P. monticola) and southwestern white pine (P. strobiformis) individuals display major gene resistance (R) to attack by C. ribicola. The resistance gene from sugar pine has been mapped using RAPD markers. Recently, genes conferring resistance to a variety of plant pathogens have been isolated from several angiosperm species. Most of the resistance genes can be placed into groups that share regions of homology, allowing resistance gene-like (RGL) sequences to be isolated using PCR primers corresponding to the shared regions. Our work indicates that RGL sequences are also present in gymnosperms. It is not unlikely that the sugar pine WPBR R gene belongs to one of the known groups of resistance gene types. We are investigating this hypothesis by cloning RGL sequences from sugar pine and determining their map positions relative to R.