Biology subjects

Frederic, S.

Publications and source records attributed to Frederic, S..

3 recordsLinked to original sources

bioRxiv2023

Is thermal aptitude a pivotal driver in the establishment of recent Puccinia striiformis f. sp. tritici lineages in Europe?

In the context of global warming, it is crucial to focus on the effects of temperature on the emergence of new lineages of endemic pathogen species, such as Puccinia striiformis f. sp. tritici (Pst) the causal agent of yellow rust on wheat. We characterized the thermal aptitude of representative isolates from the most recent common European Pst races. We assessed two key aggressiveness components - infection efficiency (IE) and latency period (LP) - under warm and cold thermal regimes, comparing 10 Pst isolates collected from 2010 to 2020 with three "old" reference isolates. The significant differences observed suggest that this species has the potential to adapt to temperature changes, but that such adaptation probably did not drive the establishment of the most recent races and the dominant Warrior and Warrior(-) they succeeded. These races display "generalist" behavior with respect to temperature, with Warrior(-) showing no more aggressiveness than the races replaced since the 1990s. The differences in competitive success between emerging Pst lineages are probably due to the deployment of resistance genes in wheat and the advantages of new forms of virulence emerging independently of thermal adaptability. However, variations in thermal adaptability for both aggressiveness components suggested an impact of geographic origin within the Warrior and Warrior(-) races, as previously reported for the "old" reference isolates. Furthermore, the independence of thermal adaptability established for IE and LP implies that the effects of temperature may depend on the stage of the epidemic (early or late), potentially modifying seasonal dynamics.

microbiology↗

bioRxiv2021

Annual dynamics of Zymoseptoria tritici populations in wheat cultivar mixtures: a compromise between the efficiency and durability of a recently broken-down resistance gene?

Cultivar mixtures slow polycyclic epidemics but may also affect the evolution of pathogen populations by diversifying the selection pressures exerted by their plant hosts at field scale. We compared the dynamics of natural populations of the fungal pathogen Zymoseptoria tritici in pure stands and in three binary mixtures of wheat cultivars (one susceptible cultivar and one cultivar carrying the recently broken-down Stb16q gene) over two annual field epidemics. We combined analyses of population size based on disease severity, and of population composition based on changes in the frequency of virulence against Stb16q in seedling assays with more than 3000 strains. Disease reductions were observed in mixtures late in the epidemic, at the whole canopy scale and on both cultivars, suggesting the existence of a reciprocal protective effect. The three cultivar proportions in the mixtures (0.25, 0.5 and 0.75) modulated the decrease in (i) the size of the pathogen population relative to the two pure stands, (ii) the size of the virulent subpopulation, and (iii) the frequency of virulence relative to the pure stand of the cultivar carrying Stb16q. Our findings suggest that optimal proportions may differ slightly between the three indicators considered. We argued potential trade-offs that should be taken into account when deploying a resistance gene in cultivar mixtures: between the dual objectives efficacy and durability, and between the size and frequency of the virulent subpopulation. Based on current knowledge, it remains unclear whether virulent subpopulation size or frequency has the largest influence on interepidemic virulence transmission.

microbiology↗

bioRxiv2017

Death of the assumption that "latent period" is fixed over the course of a plant disease epidemic

The latent period is a crucial life history trait, particularly for polycyclic plant diseases, because it determines how many complete monocycles could theoretically occur during an epidemic. Many empirical studies have focused on the variation of the latent period with pathogen or host genotype, or changes in response to environmental factors. The focus on these aspects is unsurprising, as these factors classically form the three parts of the epidemiological triangle. Experiments in controlled conditions are generally used to assess pathogenicity and host susceptibility, and also provide the opportunity to measure the distribution of latent periods in epidemiological systems. Once estimated for one or several pairs of host-pathogen genotypes, the mean value of this important trait is usually considered to be fixed and is often used \"as is\" in epidemiological models. We show here that the latent period can display non-negligible variability over the course of a disease epidemic, and that this variability has multiple sources, some of which have complex, antagonistic impacts. We develop arguments for four sources of variation that challenge the implicit assumption that the latent period remains constant: daily fluctuations in leaf temperature, nature of inoculum, host stage or age of host tissues, intra-population competition and selection for aggressiveness traits. We focus on the wheat fungal disease Septoria tritici blotch (Zymoseptoria tritici), making use of empirical datasets collected during the first authors own research projects and a targeted literature review. Such empirical epidemiological knowledge is new and potentially important for modelers. While some studies have demonstrated that the distribution of latent periods around the mean value has consequences for epidemiological dynamics, we show that it might also be important for epidemiological modelers to account for changes in this mean value during an annual epidemic. These results may be of critical importance for improving outbreak forecasting.

epidemiology↗