Our study identified a single RxLR gene whose expression varies depending on the host plant: RxLR CUST_2407 was under-expressed when the adapted isolate A infects the resistant host R and over-expressed when it infects the susceptible host S. Similar, expression-based adaptation to resistance has been described for the P. infestans RxLR effector Avr-vnt1 where the gene is only fully expressed in plants containing the cognate resistance gene, Rpi-vnt1, after the biotrophic phase and expression is weak or absent in the early stages of the infection (Stefańczyk et al., 2017). The gene discussed is RPIA; the disease is infection.