Méline Saubin

Stéphane De Mita

Fabien Halkett

Impact of ploidy and pathogen life cycle on resistance durability

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  Impact of ploidy and pathogen life cycle on resistance durability M. Saubin, S. De Mita, F. Halkett INRAE, Université de Lorraine, UMR 1136 Interactions Arbres-Microorganismes, F-54280 Champenoux, France See preprint on: https://doi.org/10.1101/2021.05.28.446112 2D Conclusion Impact of the ploidy:  Ploidy has a strong impact on evolutionary trajectories, with much greater stochasticity and delayed times of resistance breakdown for diploids. This result emphasizes the importance of genetic drift in this system: as the virulent avr allele is recessive, positive selection on resistant hosts only applies to homozygous individuals, which may lead to population collapse at low frequencies of the virulent allele. Impact of the life cycle:  With host alternation, the probability that the pathogen population collapses strongly increases with the proportion of resistant hosts in the landscape. Therefore, resistance breakdown events occurring at high proportions of resistant hosts frequently amount to evolutionary rescue.  Life cycles correspond to two selection regimes: without host alternation (soft selection) the resistance breakdown is mainly driven by the migration rate. Conversely, host alternation (hard selection) resembles an all-or-nothing game, with stochastic trajectories caused by the recurrent allele redistributions on the alternate host. Life cycle without host alternation Life cycle with host alternation Results  3 equilibria (A, B): 1) Fixation of the avirulent Higher speed of increase in the virulent avr allele for high propR (C, trajectories since the invasion Allelic and demographic trajectories since the invasion Generation 0 corresponds to the generation of invasion of the R compartment. Colored intervals correspond to the 95% confidence intervals.

  on resistance durability. A major component of host deployment strategies is the proportion of resistant hosts in the landscape (propR). Previous studies focused primarily on asexual haploid pathogens. What is the impact of the ploidy (haploid or diploid) and the pathogen's life cycle (with or without host alternation) on resistance durability? To answer this question, we modelled pathogen population dynamics and genetic evolution at the virulence (infectivity) locus. The avirulence (infectivity) gene exists at two possible states: the dominant avirulent Avr allele and the recessive virulent avr allele.