Breeding for Fungal Disease Resistance - the Use of R Genes as Transgenes in Wheat

Plant resistance (R) genes are highly effective to protect plants against diseases, but once they are prevalent in agricultural environments, pathogens mostly overcome such genes rapidly. We have tested possible strategies to make the deployment of R genes more sustainable. As a model system, we used alleles of the resistance locus Pm3 in wheat, conferring race-specific resistance to wheat powdery mildew. The alleles Pm3a, Pm3b, Pm3c, Pm3d, Pm3f or Pm3g under transcriptional control of the maize ubiquitin promoter were transformed individually into wheat to create stable R gene overexpressing lines. In field experiments, all tested transgenic lines were significantly more resistant than their respective non-transformed sister lines. Some were even more resistant than wheat lines with a natural copy of the respective Pm3 allele. We also created multilines by mixing seeds of two different transgenic Pm3 lines at a time. These Pm3 multilines were more resistant than their components when tested in the field. This demonstrates that allelic variation in a single R gene is sufficient to cause host-diversity effects and that multilines of transgenic Pm3 wheat lines represent a promising strategy for an effective and sustainable use of Pm3 alleles. Another strategy to increase disease resistance is the stacking of R genes or alleles in a single line. Therefore, we crossed transgenic Pm3 wheat lines to stably combine Pm3 alleles. Results of these experiments will be presented.