Local demographic and epidemiological patterns in theLinum marginale–Melampsora liniassociation: a multi‐year study

Abstract

Summary Many theoretical and empirical studies operate from an assumption that pathogens have a significant influence on the fecundity and life span of their host species. However, there are surprisingly little data investigating the long‐term fitness impacts and genetic consequences that arise from pathogen infection in natural populations. Here, we address this gap through the analysis of a dataset investigating the local population dynamics of a native host plant (Linum marginale) and an associated rust pathogen (Melampsora lini) across 12 years. To investigate patterns of disease prevalence and severity and track effects on host fecundity and demography, we conducted censuses on an annual basis at a single site. Annual M. lini infection prevalence ranged from 0% to 99%. Severe epidemics occurred in 3‐ to 4‐year cycles causing high overwintering mortality and subsequent changes in the relative abundance of different host phenotypes. Host population size oscillated in response to epidemics and declined towards the end of the observation period. Changes in host numbers were found to affect disease severity but not infection prevalence. Melampsora lini infection increased L. marginale fecundity; the infected plants produced threefold more seed capsules on average than uninfected plants (13·3 vs. 4·3 seed capsules per plant). To investigate how variation in environmental conditions affects epidemiology and host demography, we identified climatic factors affecting host growth, overwintering and disease severity. Winter (June) rainfall increased host overwintering success and summer (December) rainfall favoured host growth. The progress of M. lini disease epidemics benefited from optimal temperatures in February and suffered from rainfall in January. We further examined links between the genetic structure of the pathogen population and disease dynamics. There was a positive correlation between mean pathogen infectivity (as measured across a host differential set) and the severity of disease epidemics. Synthesis. Our results provide new insights into local drivers and consequences of pathogen epidemiology in natural populations. Melampsora lini infection can have profound consequences on the phenotype, demography and population structure of Linum marginale by increasing host fecundity, overwinter mortality and disease resistance.

Genetic analysis reveals long-standing population differentiation and high diversity in the rust pathogen Melampsora lini

“…lini was thought to be almost exclusively asexual in this region [ 10 , 46 ], and low levels of genetic and genotypic polymorphism have been reported in previous studies (albeit with a far lower number of markers [ 41 ]). Indeed, in contrast to theoretical expectations for asexual pathogens on epidemic growth being dominated by few genotypes [ 2 , 66 ], and our own expectations based on observations of limited pathotype diversity within epidemic development [ 67 ], our observations of high MLG diversity within years suggests that clonal spread from a small number of source genotypes is limited. Higher than expected levels of within-population diversity are consistent with some form of genetic exchange (e.g.…”

Mosaics, mixtures, rotations or pyramiding: What is the optimal strategy to deploy major gene resistance?

“…However, through mutation, the pathogen can acquire infectivity genes able to overcome the associated major resistance genes. In this work, “infectivity” is defined as in previous studies (Burdon et al., , ; Susi, Thrall, Barrett, & Burdon, ) as the qualitative ability to infect a resistant host (i.e., it is synonymous with the term ‘virulence’ in plant pathology; however, we prefer to use infectivity, as virulence has different meanings in the plant pathology, parasitology and evolutionary biology literature). Epidemics were simulated using a demogenetic model with SEIR structure (Figure a and Methods).…”

Climate change accelerates local disease extinction rates in a long‐term wild host–pathogen association

“…the 'disease triangle'; Burdon, 1987). At various stages of the life-cycle, environmental variables influence the success or failure of critical events and hence the frequency and intensity of epidemics (Burdon & Thrall, 1999;Susi, Thrall, Barrett, & Burdon, 2017). To date much of the literature regarding plant-pathogens in a warming world has focused on agricultural and forestry systems and the potential for epidemics to become more severe (Bebber et al, 2013;Chakraborty & Newton, 2011;Ghelardini et al, 2016).…”