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Phytophthora infestans Isolates Lacking Class I ipiO Variants Are Virulent on Rpi-blb1 Potato

Champouret, Nicolas, Bouwmeester, Klaas, Rietman, Hendrik, Lee, Theo van der, Maliepaard, Chris, Heupink, Anika, Vondervoort, Peter J.I. van de, Jacobsen, Evert, Visser, Richard G.F., Vossen, Edwin A.G. van der, Govers, Francine, Vleeshouwers, Vivianne G.A.A.
Molecular plant-microbe interactions 2009 v.22 no.12 pp. 1535-1545
Solanum tuberosum, potatoes, Phytophthora infestans, fungal diseases of plants, virulence, mutants, strains, disease resistance, genetic resistance, genes, introgression, genetic variation, fungal proteins, cell death, Nicotiana benthamiana, amino acid sequences, microbial genetics
A strategy to control the devastating late blight disease is providing potato cultivars with genes that are effective in resistance to a broad spectrum of Phytophthora infestans isolates. Thus far, most late blight resistance (R) genes that were introgressed in potato were quickly defeated. In contrast, the Rpi-blb1 gene originating from Solanum bulbocastanum has performed as an exclusive broad-spectrum R gene for many years. Recently, the RXLR effector family ipiO was identified to contain Avr-blb1. Monitoring the genetic diversity of the ipiO family in a large set of isolates of P. infestans and related species resulted in 16 ipiO variants in three distinct classes. Class I and class II but not class III ipiO variants induce cell death when coinfiltrated with Rpi-blb1 in Nicotiana benthamiana. Class I is highly diverse and is represented in all analyzed P. infestans isolates except two Mexican P. infestans isolates, and these were found virulent on Rpi-blb1 plants. In its C-terminal domain, IPI-O contains a W motif that is essential for triggering Rpi-blb1–mediated cell death and is under positive selection. This study shows that profiling the variation of Avr-blb1 within a P. infestans population is instrumental for predicting the effectiveness of Rpi-blb1–mediated resistance in potato.