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Abstract
There is now a very long history of genetics/breeding for disease resistance in annual crops. These efforts have resulted in conceptual advances and frustrations, as well as practical successes and failures. This talk will review this history and its relevance to the genetics of resistance in forest species. All plant breeders and pathologists are familiar with boom-and-bust cycles of single major resistance genes. Though there may be occasional situations where a single-gene approach to resistance is reasonable, most interest is in finding alternatives to this approach. This is especially true of long-lived species, for which durability of resistance becomes essential.
Combinations or "pyramids" of major genes can greatly increase durability of resistance and have provided some major success stories in annual crops. The mechanisms by which pyramids contribute durability, however, still are not entirely clear, and this is of importance to potential for success of this approach. Accumulating multiple resistances in a single genotype is complicated by epistatic effects of major genes, though both phenotypic and marker approaches can reduce this difficulty to some degree. Deploying major genes in mixed populations has been highly successful in some cases, including for some woody perennials. There is considerable variation in the epidemiological effectiveness of mixtures, however, and much is yet to be learned about the mechanisms behind this variability. Concern about selection for "superraces" in host mixtures has likely been greatly overstated, and the mechanisms by which selection for multiple virulences occur are much more complex than a simplistic evaluation of "virulence costs."
Parent Publication
Citation
Mundt, Christopher C. 2012. Resistance gene management: concepts and practice. In: Sniezko, Richard A.; Yanchuk, Alvin D.; Kliejunas, John T.; Palmieri, Katharine M.; Alexander, Janice M.; Frankel, Susan J., tech. coords. 2012. Proceedings of the fourth international workshop on the genetics of host-parasite interactions in forestry: Disease and insect resistance in forest trees. Gen. Tech. Rep. PSW-GTR-240. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture. pp. 93.
