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. 2020 Sep 24;14(2):335-347.
doi: 10.1111/eva.13117. eCollection 2021 Feb.

Maintenance of variation in virulence and reproduction in populations of an agricultural plant pathogen

Anik Dutta  1 , Daniel Croll  2 , Bruce A McDonald  1 , Luke G Barrett  3
Affiliations

Maintenance of variation in virulence and reproduction in populations of an agricultural plant pathogen

Anik Dutta et al. Evol Appl. .

Abstract

Genetic diversity within pathogen populations is critically important for predicting pathogen evolution, disease outcomes and prevalence. However, we lack a good understanding of the processes maintaining genetic variation and constraints on pathogen life-history evolution. Here, we analysed interactions between 12 wheat host genotypes and 145 strains of Zymoseptoria tritici from five global populations to investigate the evolution and maintenance of variation in pathogen virulence and reproduction. We found a strong positive correlation between virulence (amount of leaf necrosis) and reproduction (pycnidia density within lesions), with substantial variation in both traits maintained within populations. On average, highly virulent isolates exhibited higher reproduction, which might increase transmission potential in agricultural fields planted to homogeneous hosts at a high density. We further showed that pathogen strains with a narrow host range (i.e. specialists) for reproduction were on average less virulent, and those with a broader host range (i.e. generalists) were on average less fecund on a given specific host. These costs associated with adaptation to different host genotypes might constrain the emergence of generalists by disrupting the directional evolution of virulence and fecundity. We conclude that selection favouring pathogen strains that are virulent across diverse hosts, coupled with selection that maximizes fecundity on specific hosts, may explain the maintenance of these pathogenicity traits within and among populations.

Keywords: Zymoseptoria tritici; host specialization; reproduction; trade‐off; virulence; wheat.

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Conflict of interest statement

None declared.

Figures

Figure 1
Figure 1
Multiple comparisons for (a) virulence (amount of necrotic lesion area) and (b) reproduction (pycnidia density within lesions) among the five Zymoseptoria tritici populations on 12 wheat hosts. Data were log‐transformed
Figure 2
Figure 2
Correlation between virulence (amount of necrotic lesion area) and reproduction (pycnidia density within lesions; (a) overall and (b) within each population, among 145 Zymoseptoria tritici isolates from five populations. Each point represents the overall mean of virulence and reproduction combined over 12 hosts. Data were log‐transformed
Figure 3
Figure 3
Correlation between (a) overall mean reproduction (pycnidia density within lesions) and reproduction specialization, and (b) overall mean virulence (amount of necrotic lesion area) and reproduction specialization, among 145 Zymoseptoria tritici isolates from five populations. Specialization represents the estimates of adjusted coefficient of variation of means across 12 hosts for each trait. Higher specialization indicates preference for specific hosts to maximize trait performance. Data were log‐transformed
Figure 4
Figure 4
Correlation between maximum reproduction (maximum pycnidia density within the lesion area produced by each isolate across 12 hosts) and reproduction specialization (measured as the adjusted coefficient of variation of means for pycnidia density within lesions across 12 hosts) among 145 Zymoseptoria tritici isolates from five populations. Data were log‐transformed
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