DOI: 10.5061/dryad.dr7sqv9xs
title: Resistance correlations influence infection by foreign pathogens

description: 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 infection ability than the endemic pathogen, infection
 outcomes are determined by the sign and strength of the regression of the
 host’s genetic variation in infection rates by a foreign pathogen on
 variation in infection rates by an endemic pathogen, and by resistance
 allele frequencies. Given that pre-invasion equilibria of resistance are
 determined by factors including resistance costs, we show that protection
 against foreign pathogens afforded by positively correlated resistances
 can be lessened or even result in elevated infection risk at the
 population level, depending on local dynamics. Therefore, a pathogen’s
 emergence potential could be influenced, not just by its average infection
 rate, but by resistance variation resulting from prior selection imposed
 by endemic diseases.
description: Seeds of <em>Silene vulgaris </em>were sampled from
 natural populations as 28 maternal half-sib families (seeds from a single
 maternal plant, but where multiple sires are possible), with two families
 from each of 14 localities.  The seed families were used for inoculation
 experiments, testing the relationship between infection rates (proportions
 that became diseased following exposure to the pathogen) for an endemic
 pathogen of <em>S. vulgaris</em> (the anther-smut pathogen
 <em>Microbotryum silenes-inflatae</em>) and a foreign pathogen
 (anther-smut pathogen <em>Microbotryum lychnidis-dioicae</em>
 that normally occurs on a different host, <em>Silene
 latifolia</em>) and a foreign necrotrophic pathogen
 (<i>Stemphylium solani</i>).  The endemic pathogen,
 <i>M. silenes-inflatae</i>,<i> </i>was collected
 as the spore contents of a diseased <i>S. vulgaris </i>flower
 from one of the populations (coordinates, 44.212, 7.672).  The foreign
 pathogen, <i>M. lychnidis-dioicae</i>, was collected from a
 diseased <i>S. latifolia </i>plant in Lamole, Italy
 (coordinates, 43.551, 11.358). The necrotrophic foliar pathogen,
 <i>Stemphylium solani</i>, was isolated from an <i>S.
 vulgaris </i>plant in the introduced range in Bernardston, MA
 (coordinates, 42.682, -72.544) and cultured on malt extract agar.  Its
 identity was confirmed by the DNA sequence of the internal transcribed
 spacer region of the ribosomal RNA (GenBank accession MN856663).  Data
 show the locations of the seed collections and the proportions of plants
 that became diseased following exposure to the pathogen or lesion size
 (cm<sup>2</sup>), also showing sample sizes.