1 Introduction Crop disease resistance breeding has long been haunted by a bitter choice. Deploy race-specific resistance (R) genes and then surrender them to rapid pathogen evolution, or inactivate susceptibility (S) genes at the cost of yield penalties. This places breeders in a perpetual cycle of passive chasing. The canonical example of mlo-mediated powdery mildew resistance proved that S-gene loss-of-function can confer durable, broad-spectrum immunity (Acevedo-Garcia et al. 2017).
