Exploration and Swiss field-testing of a viral gene for specific quantitative resistance against smuts and bunts in wheat.

The viral gene for the killer protein 4 (KP4) has been explored for its antifungal effect in genetically modified wheat to defeat specifically the seed-transmitted smut and bunt diseases. In vitro both important seed-transmitted diseases of wheat, loose smut (Ustilago tritici) and stinking smut (Tilletia caries), are susceptible to KP4, whereas all other organisms tested so far proved to be not susceptible to KP4. For studies in planta we used stinking smut as a model fungus. In greenhouse experiments, two KP4-transgenic wheat lines showed up to 30% lower symptom development as compared to the nontransgenic control. As the last step in the proof of concept, field-testing has shown for the first time increased fungal resistance of a transgene in wheat. Due to its specificity against smuts and bunts, KP4 presents a very low risk to humans and the environment. Field-testing in Switzerland is regulated by a strong law, which for research is acceptable if legally and scientifically correctly applied.

Increased field resistance to Tilletia caries provided by a specific antifungal virus gene in genetically engineered wheat.

The field performance of a viral gene in two Swiss wheat (Triticum aestivum) varieties showed 10% increased fungal resistance against Tilletia caries (stinking smut). To the best of our knowledge, this is the first report of improved resistance against any fungus in the field achieved by genetic engineering in wheat. The genetically modified wheat lines previously showed a c. 30% decrease in symptoms of T. caries in the glasshouse (Clausen, M., Kräuter, R., Schachermayr, G., Potrykus, I. and Sautter, C. (2000) Antifungal activity of a virally encoded gene in transgenic wheat. Nat. Biotechnol. 18, 446-449), depending on the fungal strain inoculated. A glasshouse experiment run in parallel to the field test, and using the same collection of T. caries, gave the same results. In a dose-response experiment with isolated fungal strains, in which the infection pressure was varied via the spore concentration, the transgene behaved as a quantitative resistance gene and shifted the S-shaped dose-response curve towards higher resistance. The transgene was shown to be highly specific for fungi of the order Ustilaginales. Tests of the transgene using cell cultures of eukaryotes, including hamster and human, showed no significant side-effects with respect to biosafety. Endogenous pathogen-related genes were also activated on fungal infection in the presence of the kp4 transgene.