Resistance correlations influence infection by foreign pathogens

Reciprocal selection promotes the specificity of host-pathogen associations and resistance polymorphisms in response to disease. However, plants and animals also vary in response to pathogen species not previously encountered in nature, with potential effects on new disease emergence. Using anther-smut disease, we show that resistance (measured as infection rates) to foreign pathogens can be correlated with standing variation in resistance to an endemic pathogen. In Silene vulgaris, genetic variation in resistance to its endemic anther-smut pathogen correlated positively with resistance variation to an anther-smut pathogen from another host, but the relationship was negative between anther-smut and a necrotrophic pathogen. We present models describing the genetic basis for assessing resistance relationships between endemic and foreign pathogens and for quantifying infection probabilities upon foreign pathogen introduction. We show that even when the foreign pathogen has a lower average...