The transgene RB renders foliar late blight susceptible potato cultivars resistant

Mollov, D.¹, M. Iorizzo^1,2, S. Wielgus³, J. Raasch³, D. Carputo², L. Frusciante² S. Austin-Phillips³, J. Jiang³ and J. Bradeen¹

¹University of Minnesota, St. Paul, MN 55108; ²University of Naples “Federico II”, Portici, Italy; ³University of Wisconsin, Madison, WI 53706

Late blight (LB) (Phytophthora infestans) of potato is the single most economically important crop disease worldwide. The RB gene, cloned from the wild potato Solanum bulbocastanum, imparts foliar blight protection against all known P. infestans races. Four cultivars, Katahdin, Russet Burbank, Dark Red Norland, and Superior, have been transformed with the RB transgene and multiple independent transformed lines have been regenerated. Resistance against P. infestans US8 was measured in replicated greenhouse (University of Wisconsin) and multi-year field (University of Minnesota) trials. In total, five of seven transformed 'Katahdin', 15 of 15 transformed 'Russet Burbank', 15 of 29 transformed 'Dark Red Norland', and three of six transformed 'Superior' lines were classified as resistant or moderately resistant. Greenhouse and field data were strongly correlated. We have developed highly sensitive RT-PCR assays specific for the RB transgene. All transformed lines, including those that are phenotypically susceptible, produce the RB transcript. Current efforts include optimization of real time RT-PCR assays to quantify the RB transcript, allowing quantitative correlation of transcript levels and resistance phenotypes. Importantly, our results clearly demonstrate that at 28 days after field inoculation with P. infestans US8, untransformed controls were totally demolished by the pathogen, while the disease does not significantly affect resistant transformed lines. RB can be successfully utilized for genetic protection against foliar LB.