Genotype, environment, and genotype by environment interactions determine quantitative resistance to leaf rust (Coleosporium asterum) in Euthamia graminifolia (Asteraceae)

Abstract

Summary• The strength and consistency of genotypic differences in disease resistance determine the potential for resistance evolution in host populations that rely on vegetative reproduction. Here we surveyed infection intensity of host genotypes across space and time to estimate genotypic and environmental effects on quantitative disease resistance.• Cloned fragments of 12 Euthamia graminifolia genotypes were grown in unweeded experimental fields and outdoor pots. Infection intensity was surveyed during 2 yr of natural infection by the non-systemic rust pathogen, Coleosporium asterum .• Five of six surveys detected infection intensity differences among genotypes, despite substantial variation in mean infection intensity across surveys. When resistance was defined relative to local pathogen density, 10 -40% of resistance variation was due to host genotype. Although two genotypes exhibited greater resistance across environments, G × E interactions in resistance were common. Furthermore, infection intensity was unrelated to host size.• We conclude that quantitative resistance level can evolve in this system and show how logistic analysis (relative to local pathogen density) can provide insight into the mechanism(s) responsible for G × E interactions in infection intensity.

Reciprocal Interaction Matrix Reveals Complex Genetic and Dose-Dependent Specificity among Coinfecting Parasites

“…However, traits that determine the outcome of host-parasite interactions often show high genetic variation in nature (e.g., host resistance: Alexander et al 1993;Grosholz 1994;Kurtz and Sauer 1999;Carius et al 2001;Koskela et al 2002;Cotter et al 2004;Salvaudon et al 2005;Laine 2007; parasite infectivity : Lively 1989;Henter 1995;Carius et al 2001;Kaltz and Shykoff 2002;Laine 2007;Vale and Little 2009). Recently, heterogeneity of the environment has been acknowledged as a potential mechanism maintaining genetic polymorphism in host resistance (e.g., Blanford et al 2003;Price et al 2004;Mitchell et al 2005;Seppälä and Jokela 2010), but its importance in maintaining genetic variation in parasites is still poorly understood (but see Fels and Kaltz 2006;Laine 2007;Vale and Little 2009;Bryner and Rigling 2011). In this study, we examined whether coinfecting parasites could introduce variation to the relative fitness of parasite genotypes through genetically specific interactions that modify infection success.…”

“…Classically, heterogeneity of the environment (e.g., temperature, resource availability) is considered as an important factor contributing to the maintenance of genetic polymorphism (reviewed by Hedrick 2006), and it has recently been suggested also to be important for maintenance of genetic variation in hostparasite interactions (reviewed by Lazzaro and Little 2009). This is because genetic variation in host resistance often interacts with environmental variation; that is, different host genotypes are most resistant in different environments (G # E interaction; e.g., Blanford et al 2003;Price et al 2004;Mitchell et al 2005;Seppälä and Jokela 2010). Thus, pathogen-mediated selection may favor different host genotypes under different environmental conditions, which promotes maintenance of genetic polymorphism in host populations.…”

The contribution of foliar endophytes to quantitative resistance to Melampsora rust

“…The genetic resistance that is induced by symbionts is likely to be quantitative because major genes are typically induced only by specific pathogens (Jones & Dangl, 2006). Yet, both ecologists (Price et al, 2004) and plant breeders (Clair, 2010) still regard quantitative resistance as the product of minor genetic interactions between host and pathogen, influenced primarily by the abiotic environment. Foliar endophytes have largely been ignored, both theoretically and practically.…”

Temperature-dependent transmission and latency ofHolospora undulata, a micronucleus-specific parasite of the ciliateParamecium caudatum

“…Finally, host and/or parasite genotypes may respond differently to different environmental conditions (Ferguson & Read 2002;Blanford et al 2003;Price et al 2004;Mitchell et al 2005). The dynamics of transmission in a population will then depend on its precise genetic composition and the profile of environmental variation.…”