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Poster: Biology & Disease Mgmt: Genetics of Resistance


Gene-For-Gene in Fusiform Rust Disease of Loblolly Pine
K. SMITH (1), D. Ence (2), D. Nelson (3), M. Yandell (2), J. Davis (4) (1) USDA Forest Service, U.S.A.; (2) University of Utah, U.S.A.; (3) USDA Forest Service, U.S.A.; (4) University of Florida, U.S.A.

The rust fungus Cronartium quercuum f.sp. fusiforme (Cqf) incites fusiform rust disease on southern pines causing loss of stem quality or death. Given that fusiform rust is a coevolved, gene-for-gene pathosystem there is potential for resistance to be overcome in the field. Nine resistance genes (Fr1-Fr9) and one avirulence gene (Avr1) have been placed on the genetic maps of loblolly pine and Cqf. More recently genomic references have become available for both the host and the fungus. Allelic-level sequence data for resistance genes and their corresponding avirulence genes would make it possible to monitor virulence in the field, guide deployment and understand local outbreaks. Toward that end work is underway in both the loblolly host and Cqf pathogen. A candidate for the Fr1 resistance gene was identified in the 22 gigabase pair, loblolly pine reference genome. This gene remains a candidate and fine mapping is currently being done to improve the loblolly genetic map in this region, as well as, identify additional resistance gene candidates from elite pine families. Research on the Cqf fungus has located a genomic interval that contains the Avr1 gene using both traditional marker sequences and high-throughput re-sequencing of progeny from of an Avr1 segregating cross. Using an improved Cqf assembly and re-sequencing of field isolates, we are attempting define the Avr1 gene and the causative mutation that led to virulence in the Avr1 mapping population.