Resistance to late blight in potato. A putative gene that suppresses R genes and is elicited by specific isolates

Eleven progenies, ten bi-parental and one selfed, of tetraploid potato were assessed for phenotypic segregation ratios of resistance to susceptible individuals against two isolates of P. infestans, one avirulent to all 11 known potato R genes (avirulent pathotype) and one virulent to eight R genes (virulent pathotype). Assuming Mendelian inheritance of independent R genes, the numbers of individuals segregating for resistance to both races could not be explained sufficiently for all progenies. However, the assumed presence of dominant, specific suppressors of the R gene function that were elicited by specific isolates of the fungus and that segregated in the host independently from R genes explained all frequencies of resistant and susceptible individuals in each of the progenies studied.