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The I Gene of Bean: A Dosage-Dependent Allele Conferring Extreme Resistance, Hypersensitive Resistance, or Spreading Vascular Necrosis in Response to the Potyvirus Bean common mosaic virus

November 2000 , Volume 13 , Number  11
Pages  1,266 - 1,270

Candace Whitmer Collmer , 1 Marcia Fisher Marston , 2 Jessica C. Taylor , 1 and Molly Jahn 3

1Department of Biological and Chemical Sciences, Wells College, Aurora, NY 13026 U.S.A.; 2Department of Biology, Roger Williams University, Bristol, RI 02809 U.S.A.; 3Department of Plant Breeding and Biometry, Cornell University, Ithaca, NY 14853 U.S.A.

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Accepted 17 July 2000.

The resistance to the potyvirus Bean common mosaic virus (BCMV) conferred by the I allele in cultivars of Phaseolus vulgaris has been characterized as dominant, and it has been associated with both immunity and a systemic vascular necrosis in infected bean plants under field, as well as controlled, conditions. In our attempts to understand more fully the nature of the interaction between bean with the I resistance allele and the pathogen BCMV, we carefully varied both I allele dosage and temperature and observed the resulting, varying resistance responses. We report here that the I allele in the bean cultivars we studied is not dominant, but rather incompletely dominant, and that the system can be manipulated to show in plants a continuum of response to BCMV that ranges from immunity or extreme resistance, to hypersensitive resistance, to systemic phloem necrosis (and subsequent plant death). We propose that the particular phenotypic outcome in bean results from a quantitative interaction between viral pathogen and plant host that can be altered to favor one or the other by manipulating I allele dosage, temperature, viral pathogen, or plant cultivar.

Additional keywords: plant virus resistance, temperature-sensitive resistance.

© 2000 The American Phytopathological Society