International audienceIndividual Plum pox virus strain M infections were monitored visually durin... more International audienceIndividual Plum pox virus strain M infections were monitored visually during one to 3 years in 18 peach plots. The spatial pattern of the disease was investigated using binary data directly or after parsing the data in quadrats of 4, 9 or 16 trees. Ordinary runs demonstrated minimal aggregation of adjacent symptomatic trees. Beta-binomial analysis indicated overdispersion of infected trees for all quadrat sizes in 15 plots and the binary power law showed that intensity of aggregation was a function of incidence. Spatial relationships among quadrats were evaluated by spatial autocorrelation and SADIE analysis. The two methods were in good agreement and showed significant aggregation in a majority of data sets. Local areas of influence of PPV spread and relationships at longer distances were further investigated. Combined results indicated a wide range of spatial patterns of PPV-M infected trees. Factors that may have influenced such patterns, like the mechanisms...
International audienceNineteen peach blocks infected by the aggressive Plum pox virus strain M we... more International audienceNineteen peach blocks infected by the aggressive Plum pox virus strain M were monitored visually during 7 to 10 years and symptomatic trees were removed every year. Annual disease incidence was low (2 to 6%) in all orchard blocks but new symptomatic trees were continuously detected, even after 7 to 10 years of uninterrupted roguing. An exploratory approach using survival modeling was developed to evaluate to what extent, tree location within orchards, orchard characteristics and disease status within the vicinity of the orchards influenced the risk for a tree to become infected through time. Twelve variables were selected from survey data and from databases created using a geographic information system. The extended Cox model fitted to our data showed a significant effect of four of the variables tested on the risk for a tree to become infected through time: The area of the orchard block, the density of planting, the distance of a tree from the edge of the orch...
BGPI : équipe 6Caractérisation d'espèces cryptiques du psylle Cacopsylla pruni, insecte vecte... more BGPI : équipe 6Caractérisation d'espèces cryptiques du psylle Cacopsylla pruni, insecte vecteur d'une maladie des Prunus. Ecologie 2010, session " Adaptation des bioagresseurs de plantes à leur environnement biotique et abiotique
Plant viral diseases, and especially the ones transmitted by aerial vectors, can cause considerab... more Plant viral diseases, and especially the ones transmitted by aerial vectors, can cause considerable yield losses. A good knowledge of the distances of spread is key to the understanding of disease dynamics. Exploratory approaches aiming at characterizing the spatiotemporal distribution of diseased plants are often used to get an insight into the distances of spread. A more powerful approach is based on stochastic spatiotemporal modelling in order to estimate the dispersal function of the disease (probability density function describing the probability for an infectious plant to infect a healthy plant at distance d). In this study, we implemented a method for estimating the dispersal function of the sharka disease. Sharka is one of the most serious diseases of stone fruit trees (Prunus sp.). It is caused by Plum pox virus (PPV, genus Potyvirus), transmitted by at least twenty different aphid species in a non persistent manner. Due to the inefficiency of insecticides and the very rare...
Characterising the spatio-temporal dynamics of pathogensin naturais key to ensuring their efficie... more Characterising the spatio-temporal dynamics of pathogensin naturais key to ensuring their efficient prevention and control. However, it is notoriously difficult to estimate dispersal parameters at scales that are relevant to real epidemics. Epidemiological surveys can provide informative data, but parameter estimation can be hampered when the timing of the epidemiological events is uncertain, and in the presence of interactions between disease spread, surveillance, and control. Further complications arise from imperfect detection of disease, and from the computationally intractable number of data on individual hosts arising from landscape-level surveys. Here, we present a Bayesian framework that overcomes these barriers by integrating over associated uncertainties in a model explicitly combining the processes of disease dispersal, surveillance and control. Using a novel computationally efficient approach to account for patch geometry, we demonstrate that disease dispersal distances ...
Plum pox virus (PPV), a member of the Potyvirus genus, is distributed worldwide and is the causal... more Plum pox virus (PPV), a member of the Potyvirus genus, is distributed worldwide and is the causal agent of the economically important sharka disease of stone-fruit trees. Recently, natural recombinant M/D isolates were found to occur in Slovakia and several European countries. Surprisingly, all the recombinant isolates identified to date showed a very close molecular relationship and shared the same position of a recombination breakpoint situated in the C terminus of the NIb gene. To verify the ability of recombinant PPV to be naturally transmitted by aphids and thus to evaluate their possible epidemiological impact, experimental transmission of temporally and geographically distant recombinant PPV isolates to different Prunus spp. (P. domestica 'Julior', P. armeniaca 'Manicot', P. persica 'GF305' and 'Montclar') was carried out using a clonal culture of Myzus persicae Sulzer under controlled conditions using a technique involving a controlled acquisition access period. The results confirmed that all the recombinant PPV isolates were transmitted by aphids; however, the transmission occurred at different rates.
National audienceThe Slovak isolate BOR-3, collected from an apricot tree in 1996, was identified... more National audienceThe Slovak isolate BOR-3, collected from an apricot tree in 1996, was identified as a natural PPV recombinant between an M and D type of Plum pox virus. Several assays were conducted to evaluate the biological properties of this isolate. The recombinant isolate was transmitted to Prunus insititia × P. domestica St. Julien no. 2 (causing intensive chlorosis), P. armeniaca cv. Manicot (leaf necrosis) and P. persica GF305 (symptomless reaction). Its capacity to be transmitted by aphids was experimentally confirmed. The isolate could be easily maintained in vitro on several susceptible Prunus spp. hosts. Closely related recombinant variants were detected in different Prunus in the initial focus in the spring of 2001. Sequence analysis showed high homology between BOR-3 and newly sequenced isolates, reaching more than 99%. All the Slovak recombinant isolates share the same recombination breakpoint. In addition, recombinants showed a close serological relationship, although the serological pattern differed from that of other Slovak PPV isolates. This demonstrates that the recombinants are viable, competitive with conventional PPV-M and D isolates and circulates throughout this locality probably via aphid activity. The present work indicates that the occurrence of recombinants within PPV isolates might be more common then previously assumed
The spatial pattern of Sharka disease, caused by Plum pox virus (PPV) strain M, was investigated ... more The spatial pattern of Sharka disease, caused by Plum pox virus (PPV) strain M, was investigated in 18 peach plots located in two areas of southern France. PPV infections were monitored visually for each individual tree during one to three consecutive years. Point pattern and correlation-type approaches were undertaken using the binary data directly or after parsing them in contiguous quadrats of 4, 9, and 16 trees. Ordinary runs generally revealed a low but variable proportion of rows with adjacent symptomatic trees. Aggregation of disease incidence was indicated by the θ parameter of the beta-binomial distribution and related indices in 15 of the 18 plots tested for at least one assessment date of each. When aggregation was detected, it was indicated at all quadrat sizes and tended to be a function of disease incidence, as shown by the binary form of Taylor's power law. Spatial analysis by distance indices (SADIE) showed a nonrandom arrangement of quadrats with infected trees ...
Cacopsylla pruni is the vector of European stone fruit yellows, a quarantine disease of Prunus tr... more Cacopsylla pruni is the vector of European stone fruit yellows, a quarantine disease of Prunus trees. Nine polymorphic microsatellite markers were developed from enriched DNA libraries. Allelic variability was assessed in a collection of 149 females obtained from five localities covering a large geographical area in France. The number of detected alleles ranged from 8 to 37. Within the localities, observed and expected heterozygosities averaged across loci ranged from 0.39 to 0.55, and from 0.68 to 0.81, respectively. A heterozygote deficiency was detected for almost all loci, possibly due to a high null allele frequency. Other possible causes of the homozygote excess (mode of reproduction, inbreeding, assortative mating or Wahlund effect) are discussed. These variable microsatellite loci can provide tools to assess overall genetic variation in this important vector species. They will be used to search for population structure and migration patterns of C. pruni.
The genetic diversity of three temperate fruit tree phytoplasmas ‘Candidatus Phytoplasma prunorum... more The genetic diversity of three temperate fruit tree phytoplasmas ‘Candidatus Phytoplasma prunorum’, ‘Ca. P. mali’ and ‘Ca. P. pyri’ has been established by multilocus sequence analysis. Among the four genetic loci used, the genes imp and aceF distinguished 30 and 24 genotypes, respectively, and showed the highest variability. Percentage of substitution for imp ranged from 50 to 68 % according to species. Percentage of substitution varied between 9 and 12 % for aceF, whereas it was between 5 and 6 % for pnp and secY. In the case of ‘Ca P. prunorum’ the three most prevalent aceF genotypes were detected in both plants and insect vectors, confirming that the prevalent isolates are propagated by insects. The four isolates known to be hypo-virulent had the same aceF sequence, indicating a possible monophyletic origin. Haplotype network reconstructed by eBURST revealed that among the 34 haplotypes of ‘Ca. P. prunorum’, the four hypo-virulent isolates also grouped together in the same clade...
The complex structure of virus populations has been the object of intensive study in bacteria, an... more The complex structure of virus populations has been the object of intensive study in bacteria, animals, and plants for over a decade. While it is clear that tremendous genetic diversity is rapidly generated during viral replication, the distribution of this diversity within a single host remains an obscure area in this field of science. Among animal viruses, only Human immunodeficiency virus and Hepatitis C virus populations have recently been thoroughly investigated at an intrahost level, where they are structured as metapopulations, demonstrating that the host cannot be considered simply as a “bag” containing a homogeneous or unstructured swarm of mutant viral genomes. In plants, a few reports suggested a possible heterogeneous distribution of virus variants at different locations within the host but provided no clues as to how this heterogeneity is structured. Here, we report the most exhaustive study of the structure and evolution of a virus population ever reported at the intra...
Mapping and analyzing the disease status of individual plants within a study area at successive d... more Mapping and analyzing the disease status of individual plants within a study area at successive dates can give insight into the processes involved in the spread of a disease. We propose a permutation method to analyze such spatiotemporal maps of binary data (healthy or diseased plants) in regularly spaced plantings. It requires little prior information on the causes of disease spread and handles missing plants and censored data. A Monte Carlo test is used to assess whether the location of newly diseased plants is independent of the location of previously diseased plants. The test takes account of the significant spatial structures at each date in order to separate nonrandomness caused by the structure at one date from nonrandomness caused by the dependence between newly diseased plants and previously diseased plants. If there is a nonrandom structure at both dates, independent patterns are simulated by randomly shifting the entire pattern observed at the second date. Otherwise, inde...
Understanding at which spatiotemporal scale a disease causes significant secondary spread has bot... more Understanding at which spatiotemporal scale a disease causes significant secondary spread has both theoretical and practical implications. We investigated this issue in the case of European stone fruit yellows (ESFY), a quarantine vector-borne phytoplasma disease of Prunus trees. Our work was focused on the processes underlying disease spread: the interplay between the life cycles of the pathogen ('Candidatus Phytoplasma prunorum') and of the vector (Cacopsylla pruni). We demonstrated experimentally that C. pruni has only one generation per year and we showed that, at least in southeastern France, C. pruni migrates between conifers in mountainous regions (where it overwinters) and Prunus spp. at lower altitude (where it breeds). In acquisition-inoculation experiments performed with C. pruni over its period of presence on Prunus spp., both immature and mature C. pruni were hardly infectious (0.6%) despite effective phytoplasma acquisition and multiplication. We demonstrated...
International audienceIndividual Plum pox virus strain M infections were monitored visually durin... more International audienceIndividual Plum pox virus strain M infections were monitored visually during one to 3 years in 18 peach plots. The spatial pattern of the disease was investigated using binary data directly or after parsing the data in quadrats of 4, 9 or 16 trees. Ordinary runs demonstrated minimal aggregation of adjacent symptomatic trees. Beta-binomial analysis indicated overdispersion of infected trees for all quadrat sizes in 15 plots and the binary power law showed that intensity of aggregation was a function of incidence. Spatial relationships among quadrats were evaluated by spatial autocorrelation and SADIE analysis. The two methods were in good agreement and showed significant aggregation in a majority of data sets. Local areas of influence of PPV spread and relationships at longer distances were further investigated. Combined results indicated a wide range of spatial patterns of PPV-M infected trees. Factors that may have influenced such patterns, like the mechanisms...
International audienceNineteen peach blocks infected by the aggressive Plum pox virus strain M we... more International audienceNineteen peach blocks infected by the aggressive Plum pox virus strain M were monitored visually during 7 to 10 years and symptomatic trees were removed every year. Annual disease incidence was low (2 to 6%) in all orchard blocks but new symptomatic trees were continuously detected, even after 7 to 10 years of uninterrupted roguing. An exploratory approach using survival modeling was developed to evaluate to what extent, tree location within orchards, orchard characteristics and disease status within the vicinity of the orchards influenced the risk for a tree to become infected through time. Twelve variables were selected from survey data and from databases created using a geographic information system. The extended Cox model fitted to our data showed a significant effect of four of the variables tested on the risk for a tree to become infected through time: The area of the orchard block, the density of planting, the distance of a tree from the edge of the orch...
BGPI : équipe 6Caractérisation d'espèces cryptiques du psylle Cacopsylla pruni, insecte vecte... more BGPI : équipe 6Caractérisation d'espèces cryptiques du psylle Cacopsylla pruni, insecte vecteur d'une maladie des Prunus. Ecologie 2010, session " Adaptation des bioagresseurs de plantes à leur environnement biotique et abiotique
Plant viral diseases, and especially the ones transmitted by aerial vectors, can cause considerab... more Plant viral diseases, and especially the ones transmitted by aerial vectors, can cause considerable yield losses. A good knowledge of the distances of spread is key to the understanding of disease dynamics. Exploratory approaches aiming at characterizing the spatiotemporal distribution of diseased plants are often used to get an insight into the distances of spread. A more powerful approach is based on stochastic spatiotemporal modelling in order to estimate the dispersal function of the disease (probability density function describing the probability for an infectious plant to infect a healthy plant at distance d). In this study, we implemented a method for estimating the dispersal function of the sharka disease. Sharka is one of the most serious diseases of stone fruit trees (Prunus sp.). It is caused by Plum pox virus (PPV, genus Potyvirus), transmitted by at least twenty different aphid species in a non persistent manner. Due to the inefficiency of insecticides and the very rare...
Characterising the spatio-temporal dynamics of pathogensin naturais key to ensuring their efficie... more Characterising the spatio-temporal dynamics of pathogensin naturais key to ensuring their efficient prevention and control. However, it is notoriously difficult to estimate dispersal parameters at scales that are relevant to real epidemics. Epidemiological surveys can provide informative data, but parameter estimation can be hampered when the timing of the epidemiological events is uncertain, and in the presence of interactions between disease spread, surveillance, and control. Further complications arise from imperfect detection of disease, and from the computationally intractable number of data on individual hosts arising from landscape-level surveys. Here, we present a Bayesian framework that overcomes these barriers by integrating over associated uncertainties in a model explicitly combining the processes of disease dispersal, surveillance and control. Using a novel computationally efficient approach to account for patch geometry, we demonstrate that disease dispersal distances ...
Plum pox virus (PPV), a member of the Potyvirus genus, is distributed worldwide and is the causal... more Plum pox virus (PPV), a member of the Potyvirus genus, is distributed worldwide and is the causal agent of the economically important sharka disease of stone-fruit trees. Recently, natural recombinant M/D isolates were found to occur in Slovakia and several European countries. Surprisingly, all the recombinant isolates identified to date showed a very close molecular relationship and shared the same position of a recombination breakpoint situated in the C terminus of the NIb gene. To verify the ability of recombinant PPV to be naturally transmitted by aphids and thus to evaluate their possible epidemiological impact, experimental transmission of temporally and geographically distant recombinant PPV isolates to different Prunus spp. (P. domestica 'Julior', P. armeniaca 'Manicot', P. persica 'GF305' and 'Montclar') was carried out using a clonal culture of Myzus persicae Sulzer under controlled conditions using a technique involving a controlled acquisition access period. The results confirmed that all the recombinant PPV isolates were transmitted by aphids; however, the transmission occurred at different rates.
National audienceThe Slovak isolate BOR-3, collected from an apricot tree in 1996, was identified... more National audienceThe Slovak isolate BOR-3, collected from an apricot tree in 1996, was identified as a natural PPV recombinant between an M and D type of Plum pox virus. Several assays were conducted to evaluate the biological properties of this isolate. The recombinant isolate was transmitted to Prunus insititia × P. domestica St. Julien no. 2 (causing intensive chlorosis), P. armeniaca cv. Manicot (leaf necrosis) and P. persica GF305 (symptomless reaction). Its capacity to be transmitted by aphids was experimentally confirmed. The isolate could be easily maintained in vitro on several susceptible Prunus spp. hosts. Closely related recombinant variants were detected in different Prunus in the initial focus in the spring of 2001. Sequence analysis showed high homology between BOR-3 and newly sequenced isolates, reaching more than 99%. All the Slovak recombinant isolates share the same recombination breakpoint. In addition, recombinants showed a close serological relationship, although the serological pattern differed from that of other Slovak PPV isolates. This demonstrates that the recombinants are viable, competitive with conventional PPV-M and D isolates and circulates throughout this locality probably via aphid activity. The present work indicates that the occurrence of recombinants within PPV isolates might be more common then previously assumed
The spatial pattern of Sharka disease, caused by Plum pox virus (PPV) strain M, was investigated ... more The spatial pattern of Sharka disease, caused by Plum pox virus (PPV) strain M, was investigated in 18 peach plots located in two areas of southern France. PPV infections were monitored visually for each individual tree during one to three consecutive years. Point pattern and correlation-type approaches were undertaken using the binary data directly or after parsing them in contiguous quadrats of 4, 9, and 16 trees. Ordinary runs generally revealed a low but variable proportion of rows with adjacent symptomatic trees. Aggregation of disease incidence was indicated by the θ parameter of the beta-binomial distribution and related indices in 15 of the 18 plots tested for at least one assessment date of each. When aggregation was detected, it was indicated at all quadrat sizes and tended to be a function of disease incidence, as shown by the binary form of Taylor's power law. Spatial analysis by distance indices (SADIE) showed a nonrandom arrangement of quadrats with infected trees ...
Cacopsylla pruni is the vector of European stone fruit yellows, a quarantine disease of Prunus tr... more Cacopsylla pruni is the vector of European stone fruit yellows, a quarantine disease of Prunus trees. Nine polymorphic microsatellite markers were developed from enriched DNA libraries. Allelic variability was assessed in a collection of 149 females obtained from five localities covering a large geographical area in France. The number of detected alleles ranged from 8 to 37. Within the localities, observed and expected heterozygosities averaged across loci ranged from 0.39 to 0.55, and from 0.68 to 0.81, respectively. A heterozygote deficiency was detected for almost all loci, possibly due to a high null allele frequency. Other possible causes of the homozygote excess (mode of reproduction, inbreeding, assortative mating or Wahlund effect) are discussed. These variable microsatellite loci can provide tools to assess overall genetic variation in this important vector species. They will be used to search for population structure and migration patterns of C. pruni.
The genetic diversity of three temperate fruit tree phytoplasmas ‘Candidatus Phytoplasma prunorum... more The genetic diversity of three temperate fruit tree phytoplasmas ‘Candidatus Phytoplasma prunorum’, ‘Ca. P. mali’ and ‘Ca. P. pyri’ has been established by multilocus sequence analysis. Among the four genetic loci used, the genes imp and aceF distinguished 30 and 24 genotypes, respectively, and showed the highest variability. Percentage of substitution for imp ranged from 50 to 68 % according to species. Percentage of substitution varied between 9 and 12 % for aceF, whereas it was between 5 and 6 % for pnp and secY. In the case of ‘Ca P. prunorum’ the three most prevalent aceF genotypes were detected in both plants and insect vectors, confirming that the prevalent isolates are propagated by insects. The four isolates known to be hypo-virulent had the same aceF sequence, indicating a possible monophyletic origin. Haplotype network reconstructed by eBURST revealed that among the 34 haplotypes of ‘Ca. P. prunorum’, the four hypo-virulent isolates also grouped together in the same clade...
The complex structure of virus populations has been the object of intensive study in bacteria, an... more The complex structure of virus populations has been the object of intensive study in bacteria, animals, and plants for over a decade. While it is clear that tremendous genetic diversity is rapidly generated during viral replication, the distribution of this diversity within a single host remains an obscure area in this field of science. Among animal viruses, only Human immunodeficiency virus and Hepatitis C virus populations have recently been thoroughly investigated at an intrahost level, where they are structured as metapopulations, demonstrating that the host cannot be considered simply as a “bag” containing a homogeneous or unstructured swarm of mutant viral genomes. In plants, a few reports suggested a possible heterogeneous distribution of virus variants at different locations within the host but provided no clues as to how this heterogeneity is structured. Here, we report the most exhaustive study of the structure and evolution of a virus population ever reported at the intra...
Mapping and analyzing the disease status of individual plants within a study area at successive d... more Mapping and analyzing the disease status of individual plants within a study area at successive dates can give insight into the processes involved in the spread of a disease. We propose a permutation method to analyze such spatiotemporal maps of binary data (healthy or diseased plants) in regularly spaced plantings. It requires little prior information on the causes of disease spread and handles missing plants and censored data. A Monte Carlo test is used to assess whether the location of newly diseased plants is independent of the location of previously diseased plants. The test takes account of the significant spatial structures at each date in order to separate nonrandomness caused by the structure at one date from nonrandomness caused by the dependence between newly diseased plants and previously diseased plants. If there is a nonrandom structure at both dates, independent patterns are simulated by randomly shifting the entire pattern observed at the second date. Otherwise, inde...
Understanding at which spatiotemporal scale a disease causes significant secondary spread has bot... more Understanding at which spatiotemporal scale a disease causes significant secondary spread has both theoretical and practical implications. We investigated this issue in the case of European stone fruit yellows (ESFY), a quarantine vector-borne phytoplasma disease of Prunus trees. Our work was focused on the processes underlying disease spread: the interplay between the life cycles of the pathogen ('Candidatus Phytoplasma prunorum') and of the vector (Cacopsylla pruni). We demonstrated experimentally that C. pruni has only one generation per year and we showed that, at least in southeastern France, C. pruni migrates between conifers in mountainous regions (where it overwinters) and Prunus spp. at lower altitude (where it breeds). In acquisition-inoculation experiments performed with C. pruni over its period of presence on Prunus spp., both immature and mature C. pruni were hardly infectious (0.6%) despite effective phytoplasma acquisition and multiplication. We demonstrated...
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Papers by Gerard Labonne