DETECTION OF A MAJOR GENE FOR RESISTANCE TO FUSIFORM RUST DISEASE IN LOBLOLLY-PINE BY GENOMIC MAPPING

Genomic mapping has been used to identify a region of the host genome that determines resistance to fusiform rust disease in loblolly pine w here no discrete, simply inherited resistance factors had been previou sly found by conventional genetic analyses over four decades. A resist ance locus, behaving as a single dominant gene, was mapped by associat ion with genetic markers, even though the disease phenotype deviated f rom the expected Mendelian ratio. The complexity of forest pathosystem s and the limitations of genetic analysis, based solely on phenotype, had led to an assumption that effective long-term disease resistance i n trees should be polygenic. However, our data show that effective lon g-term resistance can be obtained from a single qualitative resistance gene, despite the presence of virulence in the pathogen population. T herefore, disease resistance in this endemic coevolved forest pathosys tem is not exclusively polygenic. Genomic mapping now provides a power ful tool for characterizing the genetic basis of host pathogen interac tions in forest trees and other undomesticated organisms, where conven tional genetic analysis often is limited or not feasible.