No Cost of Resistance in Wheat Gene Stack Lines Containing 10 Stem Rust Resistance Transgenes

Genetic resistance is the most economical and sustainable approach for crop protection, however, it is regularly overcome by pathogen virulence evolution. Polygenic resistance has greater durability, but unlinked genes are laborious to maintain in breeding programs. Introducing cloned resistance genes into the genome as gene stacks enables polygenic resistance with single locus inheritance. Fielder and Robin wheat plants were generated carrying two loci that each encode five wheat stem rust resistance transgenes, that is, Sr13c/Sr21/Sr22/Sr26/Sr33 and Sr22/Sr35/Sr45/Sr50/Sr55. Multiple transgenic events were combined and tested in the field. These lines, with unprecedented levels of transgenic resistance (i.e., 10 transgenes encoded on 90 kb of sequence), showed stable gene stack inheritance and transgene expression after eight generations and were highly resistant in the field. Importantly, in the absence of disease pressure no reproducible differences in the agronomic performance of transgenic lines that contained either one or both gene stacks was seen compared with control lines over two field trial seasons. These data confirm resistance gene stack efficacy and viability as a novel durable resistance strategy in agricultural crop production. Furthermore, this isogenic material that differs only by polygenic resistance provides significant insight into the broader question of the cost of disease resistance in host plants.