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Phenotypic Characterization of Potato Late Blight Resistance Mediated by the Broad-Spectrum Resistance Gene RB

February 2011 , Volume 101 , Number  2
Pages  263 - 270

Yu Chen and Dennis A. Halterman

First and second authors: Department of Plant Pathology, University of Wisconsin-Madison, Madison 53706; and second author: U.S. Department of Agriculture–Agricultural Research Service, Vegetable Crops Research Unit, Madison, WI 53706.

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Accepted for publication 24 September 2010.

The potato gene RB, cloned from the wild potato species Solanum bulbocastanum, confers partial resistance to late blight, caused by the oomycete pathogen Phytophthora infestans. In order to better characterize this partial resistance phenotype, we have compared host resistance responses mediated by RB with those mediated by the S. demissum-derived R gene R9, which confers immunity to P. infestans carrying the corresponding avirulence gene avrR9. We found that both RB and R9 genes were capable of eliciting a hypersensitive cell death response (HR). However, in RB plants, the pathogen escaped HR lesions and continued to grow beyond the inoculation sites. We also found that callose deposition was negatively correlated with resistance levels in tested plants. Transcription patterns of pathogenesis-related (PR) genes PR-1 basic, PR-2 acidic, and PR-5 indicated that P. infestans inoculation induced transcription of these defense-related genes regardless of the host genotype; however, transcription was reduced in both the susceptible and partially resistant plants later in the infection process but remained elevated in the immune host. Most interestingly, transcription of the HR-associated gene Hin1 was suppressed in both Katahdin and RB-transgenic Katahdin but not in R9 4 days after inoculation. Together, this suggests that suppression of certain defense-related genes may allow P. infestans to spread beyond the site of infection in the partially resistant host despite elicitation of hypersensitive cell death.

Additional keywords: effector triggered immunity.

This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 2011.