13 research outputs found
Evolution within a given virulence phenotype (pathotype) is driven by changes in aggressiveness: a case study of French wheat leaf rust populations
Plant pathogens are constantly evolving and adapting to their environment, including their host. Virulence alleles emerge, and then increase, and sometimes decrease in frequency within pathogen populations in response to the fluctuating selection pressures imposed by the deployment of resistance genes. In some cases, these strong selection pressures cannot fully explain the evolution observed in pathogen populations. A previous study on the French population of Puccinia triticina, the causal agent of wheat leaf rust, showed that two major pathotypes â groups of isolates with a particular combination of virulences â predominated but then declined over the 2005-2016 period. The relative dynamics and the domination of these two pathotypes â 166 317 0 and 106 314 0 â, relative to the other pathotypes present in the population at a low frequency although compatible, i.e. virulent on several varieties deployed, could not be explained solely by the frequency of Lr genes in the landscape. Within these two pathotypes, we identified two main genotypes that emerged in succession. We assessed three components of aggressiveness â infection efficiency, latency period and sporulation capacity â for 44 isolates representative of the four P. triticina pathotype-genotype combinations. We showed, for both pathotypes, that the more recent genotypes were more aggressive than the older ones. Our findings were highly consistent for the various components of aggressiveness for pathotype 166 317 0 grown on Michigan Amber â a ânaiveâ cultivar never grown in the landscape â or on Apache â a âneutralâ cultivar, which does not affect the pathotype frequency in the landscape and therefore was postulated to have no or minor selection effect on the population composition. For pathotype 106 314 0, the most recent genotype had a shorter latency period on several of the cultivars most frequently grown in the landscape, but not on âneutralâ and ânaiveâ cultivars. We conclude that the quantitative components of aggressiveness can be significant drivers of evolution in pathogen populations. A gain in aggressiveness stopped the decline in frequency of a pathotype, and subsequently allowed an increase in frequency of this pathotype in the pathogen population, providing evidence that adaptation to a changing varietal landscape not only affects virulence but can also lead to changes in aggressiveness
Evolution within a given virulence phenotype (pathotype) is driven by changes in aggressiveness: a case study of French wheat leaf rust populations
Diversity of thermal aptitude of Middle Eastern and Mediterranean Puccinia striiformis f. sp. tritici isolates from different altitude zones
The worldwide spread of wheat yellow rust lineage PstS1/S2 adapted to higher temperatures prompted us to investigate how diverse temperature responses of this lineage are in the Middle East, where diversity was previously observed within this lineage for pathotypes and genotypes. Here we highlight the diversity of response to temperature within a PstS1/S2 population. Twenty-six isolates from eight countries and different altitudes, which were tested under four combinations of cold and warm incubation and postincubation temperature conditions, showed diversity for infection efficiency (IE) and latency period (LP). IE of the various isolates ranged from 5.8% to 13.7% under cold (5°C) and 0.04% to 1% under warm (20°C) incubation temperatures. LP varied from 10.2 days under warm to 4.43 days under cold incubation. LP of isolates from the same country could differ by 2 days. Significant differences in thermal aptitudes of the isolates were observed between and within countries. IE and LP diversity was not related to altitude origin of the isolates on the whole; however, a trade-off between IE and LP was observed for isolates from low altitude (<400 m) under a warm regime. We showed diversity for thermal aptitude for IE and LP of isolates belonging to the same PstS1/S2 lineage. Understanding Pst temperature aptitude among geographically distant isolates of the same clonal lineage may help to identify the geographic range of pathogens and also to improve forecast models or breeding programmes
"IntĂ©rĂȘt de la diversitĂ© spĂ©cifique et variĂ©tale Ă lâĂ©chelle de la parcelle agricole pour limiter la progression dâune maladie : la septoriose du blĂ©"
Prix (2016) de la fondation Xavier Bernard de lâAcadĂ©mie dâagriculture de Franceil s'agit d'un type de produit dont les mĂ©tadonnĂ©es ne correspondent pas aux mĂ©tadonnĂ©es attendues dans les autres types de produit : DISSERTATION"IntĂ©rĂȘt de la diversitĂ© spĂ©cifique et variĂ©tale Ă lâĂ©chelle de la parcelle agricole pour limiter la progression dâune maladie : la septoriose du blĂ©
LâhĂ©tĂ©rogĂ©nĂ©itĂ© environnementale, un moteur de lâadaptation Ă la tempĂ©rature des populations dâagents phytopathogĂšnes foliaires ?
Les facteurs environnementaux, au premier rang desquels la tempĂ©rature, ont un impact sur la biologie des micro-organismes foliaires. Ils peuvent aussi modifier significativement leurs dynamiques populationnelles, voire leurs trajectoires Ă©volutives. Classiquement, les modĂšles Ă©pidĂ©miologiques, utilisĂ©s pour mieux gĂ©rer les maladies des plantes, intĂšgrent lâinfluence des conditions mĂ©tĂ©orologiques. Ils sâintĂ©ressent surtout Ă des rĂ©ponses et des effets moyennĂ©s, ne tenant compte ni des variations des rĂ©ponses individuelles, ni de lâhĂ©tĂ©rogĂ©nĂ©itĂ© des changements environnementaux aux Ă©chelles rĂ©ellement perçues par les agents pathogĂšnes. Ces deux niveaux de simplification sont acceptables lorsque les Ă©tats individuels et les variables continues qui leur sont associĂ©es, peu diversifiĂ©s, sont reprĂ©sentatifs de ceux de l'ensemble de la population. Il en va diffĂ©remment lorsque les populations prĂ©sentent des niveaux substantiels de variation individuelle susceptibles dâinfluencer leur capacitĂ© Ă sâadapter Ă leur environnement, et, par voie de consĂ©quence, la dynamique des Ă©pidĂ©mies sous un climat fluctuant ou changeant. Pour mettre en Ă©vidence les consĂ©quences de ces hypothĂšses rĂ©ductrices, jâai Ă©tudiĂ© comment la variation individuelle et l'hĂ©tĂ©rogĂ©nĂ©itĂ© environnementale affectent simultanĂ©ment la fitness, la composition phĂ©notypique et la rĂ©silience des populations d'un agent pathogĂšne foliaire (Zymoseptoria tritici) dans des couverts de blĂ©. Trois Ă©tapes clĂ©s ont structurĂ© lâexploration de ce cas dâĂ©tude. Tout dâabord, un protocole in vitro de phĂ©notypage haut dĂ©bit a Ă©tĂ© spĂ©cifiquement dĂ©veloppĂ©, validĂ© et utilisĂ© pour caractĂ©riser la diversitĂ© des rĂ©ponses Ă la tempĂ©rature de populations de Z. tritici Ă©chantillonnĂ©es Ă des Ă©chelles climatiques contrastĂ©es (variation spatiale et saisonniĂšre) ainsi que leurs patrons dâadaptation. Les variations environnementales spatio-temporelles rencontrĂ©es dans les couverts de blĂ©, considĂ©rĂ©es comme exerçant des pressions sĂ©lectives diffĂ©rentielles sur ces sensibilitĂ©s thermiques individuelles, ont ensuite Ă©tĂ© examinĂ©es. Enfin, la façon dont la sĂ©lection de « thermotypes » (groupes fonctionnels rassemblant des individus prĂ©sentant une mĂȘme sensibilitĂ© thermique) dĂ©termine la dynamique adaptative des populations en rĂ©ponse Ă l'hĂ©tĂ©rogĂ©nĂ©itĂ© environnementale a Ă©tĂ© Ă©tudiĂ©e. Pour cela, des approches expĂ©rimentales (in vitro, in planta et in natura) et de modĂ©lisation (in silico) ont Ă©tĂ© couplĂ©es. Elles ont notamment portĂ© sur plusieurs gĂ©nĂ©rations de populations placĂ©es dans des environnements sĂ©lectifs de plus en plus complexes. Ces travaux ont montrĂ© que le fait de nĂ©gliger l'amplitude rĂ©elle de la variation phĂ©notypique inter-individuelle d'une population microbienne et l'hĂ©tĂ©rogĂ©nĂ©itĂ© des pressions de sĂ©lection, sâexerçant des Ă©chelles phyllo- Ă mĂ©soclimatiques, conduit Ă sous-estimer la rĂ©silience de cette population, et donc son potentiel adaptatif. Les rĂ©sultats de cette thĂšse, Ă lâinterface entre Ă©pidĂ©miologie, micromĂ©tĂ©orologie et Ă©cologie, amĂ©liorent notre comprĂ©hension dâune part, de l'importance de la variation individuelle dans la dynamique adaptative des populations et, dâautre part, de la maniĂšre dont l'hĂ©tĂ©rogĂ©nĂ©itĂ© environnementale permet de maintenir des populations globalement trĂšs diverses. Elle permet finalement dâexpliquer lâexistence de patrons dâadaptation, Ă la fois Ă des Ă©chelles locales et Ă des Ă©chelles trĂšs larges, par des dynamiques adaptatives «à deux vitesses».Environmental drivers, most notably temperature, affect the biology of phyllosphere microorganisms but also induce changes in their population dynamics, even in their evolutionary trajectories. The impact of climate on foliar plant disease epidemics is usually considered in forecasting models to inform management strategies. Such models focus on averages of environmental drivers but disregard both individual variation within populations and the scale and extent of biologically relevant environmental changes. These simplifications are glossing over substantial levels of individual variation that may have important consequences on the capacity of a population to adapt to environmental changes, and thus on the dynamics of epidemics in a fluctuating or changing climate. To examine the range of validity and consequences of these simplifying assumptions, I investigated how individual variation and environmental heterogeneity jointly affect fitness, phenotypic composition and resilience of populations of a foliar pathogen (Zymoseptoria tritici) inhabiting wheat canopies. Three complementary ways of exploration were adopted in this case study. First, an in vitro high-throughput phenotyping framework was developed, validated, and used to characterise the diversity in patterns of thermal responses existing across Z. tritici populations that were sampled over contrasted scales (spatial and seasonal variation of temperature). Second, the spatio-temporal thermal variations encountered in a wheat canopy, considered as a habitat exerting fluctuating selective pressures on these differential thermal sensitivities of individuals, were investigated in depth. Third, the way selection of âthermotypesâ (functional groups of individuals displaying a similar thermal sensitivity) occurs and drives dynamics of Z. tritici populations was examined. To this end, both empirical (in vitro, in planta and in natura) and theoretical (in silico) competition experiments were conducted under increasingly complex selective environments. This research work demonstrates that glossing over the natural extent of individual phenotypic diversity in a phyllosphere microbial population and over the heterogeneity of selective pressures â from phyllo- to mesoclimate â leads to underestimate the resilience of this population, and thus its adaptive potential to environmental variations. In doing so, the results of this thesis, at the interface between epidemiology, micrometeorology, and ecology, improve our understanding of how important is individual variation to population dynamics and how environmental heterogeneity allows to maintain population diversity. Finally, this thesis provides insight into how large-scale patterns and local population processes are interlinked and display a âtwo-tierâ adaptive dynamics
Environmental heterogeneity, a driver of adaptation to temperature in foliar plant pathogen populations?
Environmental drivers, most notably temperature, affect the biology of phyllosphere microorganisms but also induce changes in their population dynamics, even in their evolutionary trajectories. The impact of climate on foliar plant disease epidemics is usually considered in forecasting models to inform management strategies. Such models focus on averages of environmental drivers but disregard both individual variation within populations and the scale and extent of biologically relevant environmental changes. These simplifications are glossing over substantial levels of individual variation that may have important consequences on the capacity of a population to adapt to environmental changes, and thus on the dynamics of epidemics in a fluctuating or changing climate. To examine the range of validity and consequences of these simplifying assumptions, I investigated how individual variation and environmental heterogeneity jointly affect fitness, phenotypic composition and resilience of populations of a foliar pathogen (Zymoseptoria tritici) inhabiting wheat canopies. Three complementary ways of exploration were adopted in this case study. First, an in vitro high-throughput phenotyping framework was developed, validated, and used to characterise the diversity in patterns of thermal responses existing across Z. tritici populations that were sampled over contrasted scales (spatial and seasonal variation of temperature). Second, the spatio-temporal thermal variations encountered in a wheat canopy, considered as a habitat exerting fluctuating selective pressures on these differential thermal sensitivities of individuals, were investigated in depth. Third, the way selection of âthermotypesâ (functional groups of individuals displaying a similar thermal sensitivity) occurs and drives dynamics of Z. tritici populations was examined. To this end, both empirical (in vitro, in planta and in natura) and theoretical (in silico) competition experiments were conducted under increasingly complex selective environments. This research work demonstrates that glossing over the natural extent of individual phenotypic diversity in a phyllosphere microbial population and over the heterogeneity of selective pressures â from phyllo- to mesoclimate â leads to underestimate the resilience of this population, and thus its adaptive potential to environmental variations. In doing so, the results of this thesis, at the interface between epidemiology, micrometeorology, and ecology, improve our understanding of how important is individual variation to population dynamics and how environmental heterogeneity allows to maintain population diversity. Finally, this thesis provides insight into how large-scale patterns and local population processes are interlinked and display a âtwo-tierâ adaptive dynamics.Les facteurs environnementaux, au premier rang desquels la tempĂ©rature, ont un impact sur la biologie des micro-organismes foliaires. Ils peuvent aussi modifier significativement leurs dynamiques populationnelles, voire leurs trajectoires Ă©volutives. Classiquement, les modĂšles Ă©pidĂ©miologiques, utilisĂ©s pour mieux gĂ©rer les maladies des plantes, intĂšgrent lâinfluence des conditions mĂ©tĂ©orologiques. Ils sâintĂ©ressent surtout Ă des rĂ©ponses et des effets moyennĂ©s, ne tenant compte ni des variations des rĂ©ponses individuelles, ni de lâhĂ©tĂ©rogĂ©nĂ©itĂ© des changements environnementaux aux Ă©chelles rĂ©ellement perçues par les agents pathogĂšnes. Ces deux niveaux de simplification sont acceptables lorsque les Ă©tats individuels et les variables continues qui leur sont associĂ©es, peu diversifiĂ©s, sont reprĂ©sentatifs de ceux de l'ensemble de la population. Il en va diffĂ©remment lorsque les populations prĂ©sentent des niveaux substantiels de variation individuelle susceptibles dâinfluencer leur capacitĂ© Ă sâadapter Ă leur environnement, et, par voie de consĂ©quence, la dynamique des Ă©pidĂ©mies sous un climat fluctuant ou changeant. Pour mettre en Ă©vidence les consĂ©quences de ces hypothĂšses rĂ©ductrices, jâai Ă©tudiĂ© comment la variation individuelle et l'hĂ©tĂ©rogĂ©nĂ©itĂ© environnementale affectent simultanĂ©ment la fitness, la composition phĂ©notypique et la rĂ©silience des populations d'un agent pathogĂšne foliaire (Zymoseptoria tritici) dans des couverts de blĂ©. Trois Ă©tapes clĂ©s ont structurĂ© lâexploration de ce cas dâĂ©tude. Tout dâabord, un protocole in vitro de phĂ©notypage haut dĂ©bit a Ă©tĂ© spĂ©cifiquement dĂ©veloppĂ©, validĂ© et utilisĂ© pour caractĂ©riser la diversitĂ© des rĂ©ponses Ă la tempĂ©rature de populations de Z. tritici Ă©chantillonnĂ©es Ă des Ă©chelles climatiques contrastĂ©es (variation spatiale et saisonniĂšre) ainsi que leurs patrons dâadaptation. Les variations environnementales spatio-temporelles rencontrĂ©es dans les couverts de blĂ©, considĂ©rĂ©es comme exerçant des pressions sĂ©lectives diffĂ©rentielles sur ces sensibilitĂ©s thermiques individuelles, ont ensuite Ă©tĂ© examinĂ©es. Enfin, la façon dont la sĂ©lection de « thermotypes » (groupes fonctionnels rassemblant des individus prĂ©sentant une mĂȘme sensibilitĂ© thermique) dĂ©termine la dynamique adaptative des populations en rĂ©ponse Ă l'hĂ©tĂ©rogĂ©nĂ©itĂ© environnementale a Ă©tĂ© Ă©tudiĂ©e. Pour cela, des approches expĂ©rimentales (in vitro, in planta et in natura) et de modĂ©lisation (in silico) ont Ă©tĂ© couplĂ©es. Elles ont notamment portĂ© sur plusieurs gĂ©nĂ©rations de populations placĂ©es dans des environnements sĂ©lectifs de plus en plus complexes. Ces travaux ont montrĂ© que le fait de nĂ©gliger l'amplitude rĂ©elle de la variation phĂ©notypique inter-individuelle d'une population microbienne et l'hĂ©tĂ©rogĂ©nĂ©itĂ© des pressions de sĂ©lection, sâexerçant des Ă©chelles phyllo- Ă mĂ©soclimatiques, conduit Ă sous-estimer la rĂ©silience de cette population, et donc son potentiel adaptatif. Les rĂ©sultats de cette thĂšse, Ă lâinterface entre Ă©pidĂ©miologie, micromĂ©tĂ©orologie et Ă©cologie, amĂ©liorent notre comprĂ©hension dâune part, de l'importance de la variation individuelle dans la dynamique adaptative des populations et, dâautre part, de la maniĂšre dont l'hĂ©tĂ©rogĂ©nĂ©itĂ© environnementale permet de maintenir des populations globalement trĂšs diverses. Elle permet finalement dâexpliquer lâexistence de patrons dâadaptation, Ă la fois Ă des Ă©chelles locales et Ă des Ă©chelles trĂšs larges, par des dynamiques adaptatives «à deux vitesses»
Diversifier les paysages cultivés : état des connaissances et perspectives de recherche
International audienceDiversifier les paysages cultivés : état des connaissances et perspectives de recherche Chapitre tiré de l'ouvrage « L'immunité des plantes » Edition Quae, 2021
Diversifier les paysages cultivés : état des connaissances et perspectives de recherche
International audienceDiversifier les paysages cultivĂ©s : Ă©tat des connaissances et perspectives de recherche Chapitre 19tirĂ© de l'ouvrage « L'immunitĂ© des plantes »PrĂ©sentation de l'ouvrageLes plantes disposent dâune immunitĂ© naturelle qui leur permet de rĂ©sister aux maladies et aux agressions parasitaires dans leur environnement. Lâinvention puis le dĂ©veloppement de lâagriculture ont cependant crĂ©Ă© des milieux trĂšs favorables Ă lâĂ©mergence de nouvelles maladies et au dĂ©veloppement des Ă©pidĂ©mies. Cette vulnĂ©rabilitĂ© sanitaire sâest ensuite accentuĂ©e avec lâintensification agricole, Ă partir des annĂ©es 1950, de sorte que le recours gĂ©nĂ©ralisĂ© aux pesticides de synthĂšse est devenu un pilier essentiel de la production. Ce modĂšle est dĂ©sormais remis en cause et le dĂ©veloppement dâune protection agroĂ©cologique des cultures devient une nĂ©cessitĂ©.Comprendre comment fonctionne lâimmunitĂ© des plantes et dĂ©chiffrer leur arsenal de dĂ©fense face aux agressions parasitaires est essentiel pour produire des variĂ©tĂ©s rĂ©sistantes et rĂ©duire la dĂ©pendance de lâagriculture Ă la protection chimique. Mais il faut compter avec la formidable capacitĂ© dâadaptation des populations pathogĂšnes, qui conduit les chercheurs Ă imaginer des stratĂ©gies complexes pour maintenir efficace la rĂ©sistance des variĂ©tĂ©s cultivĂ©es. Les gĂšnes qui confĂšrent la rĂ©sistance aux plantes commencent Ă ĂȘtre perçus comme un bien commun Ă prĂ©server absolument.Cet ouvrage explicite les concepts fondamentaux et sâappuie sur des Ă©tudes de cas pour rĂ©aliser une synthĂšse trĂšs complĂšte des travaux en biologie, en modĂ©lisation et en sciences sociales sur ce quâest lâimmunitĂ© vĂ©gĂ©tale et sur la maniĂšre dont elle pourrait concourir Ă une agriculture respectueuse de lâenvironnement
Hunting for sources of durable resistance in crop cultivar evaluation data: The case of wheat yellow rust in France
International audienceAbstract Cultivar resistance is a major asset for the management of crop diseases and can play an important role in agroecological transition. However, the wide deployment of a reduced number of resistance genes can lead to a rapid adaptation of pathogen populations and to a loss of resistance efficiency. The objective of this study was to characterize and discuss different trajectories of adult plant ratings for resistance to yellow rust in French wheat cultivars between 1963 and 2018. Among 719 cultivars assessed for at least 2âyears, 590 cultivars showed no variation in their resistance scores, despite a mean of 4.3âyears and up to 33âyears of assessment. A set of descriptive variables was computed in order to compare the evolution of resistance score of 129 cultivars that experienced resistance variation. We applied a principal component analysis and a hierarchical clustering on principal components to this subdataset to constitute clusters corresponding to different cultivar profiles. Clusters C1 and C2 had small resistance variations (1â2 points on a 1â9 scale); Cluster C3 had long assessment durations and several small drops in resistance score and could be associated with quantitative resistance erosion; Cluster C4 included major drops in resistance score (4â5 points), often associated with known breakdowns of major resistance genes. Cases of limited drops in resistance score as a known resistance gene was broken down suggest the presence of efficient adult plant resistance. We discuss the use of information extracted from this dataset and methods to further explore sources of resistance to yellow rust present in French cultivars
Taking advantage of architectural diversity to improve control of splash dispersed disease in cultivar mixtures : a modelling study based on field experimentation
oral communication abstractUsing cultivar mixtures, i.e. growing several cultivars with different resistance traits in a same field, allows protection of susceptible cultivars and fungicide use reduction. Protective mixture effect against splash dispersed diseases such as septoria tritici blotch is variable depending on environmental conditions. Understanding disease reduction mechanisms is critical for improvement of mixture design and efficiency. Major mechanisms are related to modification of disease dispersal patterns within the mixture. Increased distance between two susceptible plants reduces spore transfer, while the presence of resistant plants provides a barrier to spore dispersal. Common mixture design recommendations include choice of cultivars with similar architecture in order to constitute homogeneous canopies which should minimize competition and ease agronomical management. However, no information is available on the possible impact of mixing cultivars with contrasted architecture on disease dispersal. We used a mechanistic modelling approach based on experimental results to characterize splash dispersal patterns in wheat cultivar mixtures with either uniform (homogeneous canopies) or contrasted straw height (heterogeneous canopies). We then performed numerical experiments to study the impact of variations in location of susceptible and resistant tissues within the canopy. Dispersal events were simulated based on field observations. Chosen rain dispersal events occurred during the post-flowering phase of wheat cycle, where disease develops on top leaves and reduces yield. At this stage, canopy structure is fully developed and fixed. Architectural measurements of individual plants were used to reconstruct static 3D mockups of pure stands and mixed canopies. Mockups provided information on resistant and susceptible tissue location within the canopies and were used to compute splash dispersal. Model inputs also included leaf disease severity and rain characteristics measured during studied dispersal events. Simulated spore dispersal was consistent with spore fluxes measured in the field. Disease reduction mechanisms that are specific to heterogeneous canopies were identified. Upper leaves of the tall cultivar acted as umbrellas by intercepting raindrops and reducing splash on diseased leaves at the bottom of the canopy. On the other hand, contaminated splash droplets produced at the same location were trapped by leaves of the lowest cultivar, thus reducing contamination of upper leaves of the tallest cultivar. Modelling results allowed quantification and hierarchisation of dispersal processes occurring in heterogeneous mixed canopies and outlined the importance of the location of resistant and susceptible organs within the canopy