Detection of a major gene for resistance to fusiform rust disease in loblolly pine by genomic mapping.

Abstract

Genomic mapping has been used to identify a region of the host genome that determines resistance to fusiform rust disease in loblolly pine where no discrete, simply inherited resistance factors had been previously found by conventional genetic analysis over four decades. A resistance locus, behaving as a single dominant gene, was mapped by association with genetic markers, even though the disease phenotype deviated from the expected Mendelian ratio. The complexity of forest pathosystems and the limitations of genetic analysis, based solely on phenotype, had led to an assumption that effective long-term disease resistance in trees should be polygenic. However, our data show that effective long-term resistance can be obtained from a single qualitative resistance gene, despite the presence of virulence in the pathogen population. Therefore, disease resistance in this endemic coevolved forest pathosystem is not exclusively polygenic. Genomic mapping now provides a powerful tool for characterizing the genetic basis of host pathogen interactions in forest trees and other undomesticated, organisms, where conventional genetic analysis often is limited or not feasible.

Genetic and physical mapping of Melampsora rust resistance genes in Populus and characterization of linkage disequilibrium and flanking genomic sequence

“…in poplar ( Hsiang & Van Der Kamp, 1985;Cervera et al ., 1996;Lefevre et al ., 1998). Molecular markers have been identified that are tightly linked to several disease-resistance loci ( Devey et al ., 1995;Wilcox et al ., 1996;Lefevre et al ., 1998;Stirling et al ., 2001), but resistance genes have yet to be cloned and functionally characterized for a forest tree.…”

Identification of Nine Pathotype-Specific Genes Conferring Resistance to Fusiform Rust in Loblolly Pine (Pinus taeda L.)

“…Wilcox et al [19] previously identified and verified the existence of this pathotype-specific resistance gene via genetic mapping. Genetic mapping information for all the currently identified Fr genes is discussed in Section 3.2.…”

“…The families were either progeny from selections that are property of privately-owned industrial tree improvement programs, or progeny from selections from public (USDA Forest Service and Georgia Forestry Commission) tree improvement programs. Private industry-owned selections have been assigned a generic single-letter code (except for selection 10-5, which was previously used to map Fr1 [19]) to keep their identity anonymous. Publicly-owned materials are identified by their original tree improvement code.…”

“…In this paper we used a gene-for-gene approach to provide an analysis of seven loblolly pine families challenged with inocula derived from five single-genotype isolates of the fusiform rust fungus, leading, along with the work of Wilcox et al [19], to the identification and genetic mapping of nine pathotype-specific fusiform rust resistance genes (Fr genes). These results are discussed in the context of pathosystem biology, forest management, and tree improvement.…”

“…Powers [16] and Kuhlman and Matthews [17] reported methods for the development of single-genotype Cqf isolates with the Kuhlman and Matthews work showing virulence variation among single-genotype isolates derived from the same single gall. Contemporaneous with and subsequent to Kuhlman and Matthews [17], the use of basidiospore inocula derived from single-genotype isolates has greatly advanced the understanding of the genetics of fusiform rust disease, and the hypothesis that this pathosystem largely conforms to a classic gene-for-gene model has yet to be rejected [18][19][20][21][22][23][24][25]. Recently, Nelson et al [26] concluded that gene-for-gene interactions largely determine fusiform rust gall formation in loblolly and slash pine, with that conclusion being firmly supported for loblolly pine by the demonstration that host resistance gene Fr1 and pathogen avirulence gene Avr1 interact in a gene-for-gene fashion [27].…”