Papers by Suffert Frédéric
Trends in Ecology and Evolution, 2007
Fungi represent an essential component of biodiversity, not only because of the large number of s... more Fungi represent an essential component of biodiversity, not only because of the large number of species, but also for their ecological, evolutionary and socio-economic significance. Yet, until recently, fungi received scant consideration in ecology, especially invasion ecology. Their under-representation is largely the result of a lack of scientific knowledge of fungal biodiversity and ecology. With the exception of pathogenic fungi, which cause emergent infectious diseases, the impact of fungal invasions is often difficult to quantify owing to limited baseline data on fungal communities. Here, we aim to raise awareness among mycologists and ecologists of the fungal dimension of invasions and of the need to intensify research in fungal ecology to address issues of future introductions.
European Journal of Plant Pathology, 2008
Carrot cavity spot (CCS) is one of the most important soilborne diseases affecting the carrot cro... more Carrot cavity spot (CCS) is one of the most important soilborne diseases affecting the carrot crop. The few epidemiological studies that have investigated the temporal and spatial dynamics of the disease have been based solely on diagrammatic scales or semi-quantitative indices. To reveal epidemiological processes involved in the development of CCS epidemics, we investigated pathometric relationships. To this end, standardised measurements were defined (disease incidence i, lesion density d, conditional lesion density cd, lesion size ls, and total diseased area tda). The evolution of a cohort of CCS lesions according to their size suggested that lesions can expand over time. Two pathometric relationships were tested: a first one, between i and tda, is given by the equation i = 100(1−exp(−a(t)tda)), where t is thermal time, and a second one, between tda, d, and ls, is given by the equation tda = c(t)πd(ls/2)2. These relationships were validated for CCS epidemics in the case of field experiments, a survey in commercial fields, and a controlled-conditions experiment. The temporal linear decrease of the time-dependent parameter a(t) in the first relationship suggested that CCS epidemics followed classical epidemiological phases driven by successive processes: (1) the mobilisation of soil inoculum leading to primary infection, (2) the spread of disease to neighbouring taproots (alloinfection), and (3) the intensification of disease on the taproot (autoinfection). This is consistent with complementary experimental results which demonstrated that auto- and alloinfections occur in CCS epidemics.
Food Security, 2009
Malevolent use of plant pathogens in an act of agroterrorism represents a potential threat for Eu... more Malevolent use of plant pathogens in an act of agroterrorism represents a potential threat for European agriculture and forestry. We investigated the risk of agroterrorism sensu lato, which is raising debates among the community of plant pathologists. In the absence of a previous unambiguous definition of agroterrorism we characterized the risk for Europe by taking into account the multiplicity of the threat, of the perpetrator’s objectives, and of potential modus operandi. To this end, we have applied a three-step methodology involving: (1) the building of a list of candidate pathogens, (2) a scenario-based exploration of potential agroterrorist acts, and (3) the design of a risk evaluation scheme (RES), derived from the standard pest risk analysis (PRA). We adopted a congruent risk assessment strategy consisting of coupling the foresight exercise (assignment of nine key pathogens extracted from the list to nine scenarios and comparison of different intrinsic criteria) to the analytical assessment (application of the RES to the nine key pathogens and qualitative analysis resulting in a pentagonal star plot representing risk profiles). Analysis was performed by non-experts on the selected diseases, and thus enabled a comparison between crops or pathogens on the basis of the characterization of the threat. The risk, considered in its hybrid dimension (both factual because it refers to crop protection and an effective stake, and also irrational because it refers to bioterrorism, a vague and unobservable concept) was characterized exhaustively for the selected plant pathogens and the success of a malevolent act appeared to be much more uncertain than believed. However, agroterrorism should be considered as a plausible threat, potentially more important by the consequences of the securitization of the concept, which could imply disruption of regulations and trade, than by direct damaging consequences on European crops. There is probably not a single short-list of threatening pathogens: different pathogens would be most threatening for different purposes, for different perpetrators, and for different target crops.
Plant Pathology, 2007
The relative importance of primary and secondary infections (auto- and alloinfections) in the dev... more The relative importance of primary and secondary infections (auto- and alloinfections) in the development of a carrot cavity spot (CCS) epidemic caused by Pythium spp. were investigated. Three cropping factors: fungicide application, soil moisture and planting density, were selected as the key variables affecting the disease tetrahedron. Their effects on: (i) disease measurements at a specific time, (ii) the areas under the disease progress curves (AUDPCs) and (iii) a time-dependent parameter in a pathometric incidence-severity relationship, were studied. Mefenoxam applications 5 and 9 weeks after sowing reduced the intensity of a field CCS epidemic that involved both primary and secondary infections. In microcosm experiments, mefenoxam reduced secondary infections by Pythium violae obtained by transplanting infected carrot roots and slowed disease progress (1·6 lesions per root in treated versus 5·8 lesions in non-treated microcosms). A deficit of soil moisture limited the movement of Pythium propagules to host tissue, and thus reduced primary infections in the field; it also promoted the healing of lesions, limiting lesion expansion and the potential for alloinfections (6·8–7·5 lesions per root in irrigated plots compared with 2·4 lesions in non-irrigated plots). A negative relationship between the mean root-to-root distance and the rate of alloinfections was established in microcosms; a reduction in mean planting density was also effective in limiting CCS development (0·5, 1·6 and 2·0 lesions per root in microcosms containing 8, 16 and 31 roots, respectively). An integrated disease management system based on a combination of cultural methods, such as optimized fungicide application, date of harvest versus soil moisture content, and host density versus planting pattern, may make a useful contribute to the control of CCS.
Canadian Journal of Plant Pathology-revue Canadienne De Phytopathologie, 2007
Carrot cavity spot is caused by a complex of pathogens belonging to the genus Pythium, including ... more Carrot cavity spot is caused by a complex of pathogens belonging to the genus Pythium, including Pythium violae. The disease is characterized by the appearance of sunken elliptical lesions on the taproot. The objective of the present study is to identify, understand, and prioritize the processes that induce the spatio-temporal kinetics of epidemics of cavity spot. We favoured the hypothesis that considers primary infection (from soilborne inoculum) and secondary infection (root-to-root contaminations from existing lesions, i.e., auto- and allo-infections). Epidemics were obtained during a 3-year field experiment after artificial soil infestation of plots with P. violae at increasing inoculum doses. Different kinetics of cavity spot were described using standardized disease measurements. The analysis of the incidence curves showed the early appearance of a plateau, with differences in the disease level that are positively correlated with the inoculum doses. These differences disappeared at the end of the cropping season. Three simulation models, integrating or not the concomitance of the primary and secondary infections, were fitted to the disease incidence to test if progress curves were compatible with the hypothesis of the occurrence of both infection processes: the logistic model, the bilogistic model of Hau and Amorim, and the model of Brassett and Gilligan without temporal decline of the soil inoculum potential. The quality of the fitting was correct in the three cases, and the hypothesis of the occurrence of secondary infections was not refuted. This result is an important argument to demonstrate the polycyclic nature of the disease.
Est posée dans ce texte la question de ce que revêt la notion d'« intégration de méthodes de lutt... more Est posée dans ce texte la question de ce que revêt la notion d'« intégration de méthodes de lutte » en protection des cultures et le vocabulaire avec lequel il est possible de décrire et d'estimer ce caractère intégratif. Le terme « complémentarité », auquel nous préférons le terme générique « complémentation », est largement employé dans la littérature et recouvre plusieurs fonctionnalités. Il peut tour à tour signifier « complémentarité » au sens strict, « additivité », « compatibilité » ou « supplétivité », termes pour chacun desquels nous proposons une définition fonctionnelle ainsi que quelques exemples pratiques, essentiellement empruntés au domaine de l'épidémiologie végétale. Des méthodes de lutte se « complémentent » lorsque leur application combinée est basée sur -ou aboutit à -un « complément » bénéfique, c'est-à-dire une conséquence positive en termes de moyens ou de résultats. Les éléments qui poussent à distinguer et définir différents types de « complémentation » sont liés aux conséquences, à la nature, voire à l'origine de la combinaison de méthodes.
Applied Soil Ecology, 2007
Carrot cavity spot (CCS) is characterised by the appearance of small sunken elliptical lesions on... more Carrot cavity spot (CCS) is characterised by the appearance of small sunken elliptical lesions on the tap root. It is caused by a complex of Pythium species, but the species diversity and interactions within the complex have never been studied for modelling CCS epidemics. The diversity of a pathogenic Pythium community was assessed during 3 consecutive years in a field experiment after an initial artificial soil infestation with P. violae. 1241 lesions were examined, yielding 728 Pythium isolates. Conventional microbiological methods and restriction polymorphism of the internal transcribed spacer regions of the rDNA of 209 representative Pythium isolates allowed us to identify 655 isolates as belonging to six Pythium species, including P. violae and five indigenous species (P. sulcatum, P. intermedium, P. sylvaticum/irregulare, P. coloratum, and P. ultimum). Biological traits, such as pathogenicity, optimum temperature for mycelial growth and saprophytic survival of the inoculum, explained the fluctuations in the composition of the complex over 17 successive samplings during the 3-year period, most notably the prevalence of first P. violae and then P. sulcatum. P. violae and P. sulcatum were occasionally isolated in mixture from single lesions (10.4% and 9.6%, respectively). Other species were more frequently isolated in mixture: 30.8% for P. intermedium, 33.8% for P. sylvaticum/ irregulare, 42.9% for P. ultimum, and 66.7% for P. coloratum. A contingency analysis allowed us to define 'major' and 'minor' species on both pathological and ecological criteria (frequency of occurrence in the complex, pathogenicity and ability to induce lesions by themselves), and demonstrated that infection by one 'major' pathogen species (P. violae or P. sulcatum) is not positively correlated with the presence of a second Pythium species. The ratio between 'observed' and 'expected' mixed infection frequency under the assumption of independent infection (mir) was less than 1 for P. violae, P. sulcatum, P. intermedium, and P. sylvaticum/ irregulare (P < 0.05). For all Pythium species, there was a negative linear relationship between mir and pathogenicity (R 2 = 0.638): the less a Pythium species was pathogenic on carrot, the more often it was isolated from a CCS lesion in mixture with at least one other species. The non-significance of interactions between species during the infection phase suggests that CCS epidemics can be analysed as if they were caused by a single Pythium species. #
Journal of General Plant Pathology, 2008
Carrot cavity spot, caused by a complex of Pythium species, is characterized by sunken elliptical... more Carrot cavity spot, caused by a complex of Pythium species, is characterized by sunken elliptical lesions on the taproot. Recent epidemiological studies of P. violae have demonstrated the occurrence of both primary and secondary infections, with two types of secondary infection, autoinfection and alloinfection. Investigating the mechanisms underlying alloinfection and the role of carrot lateral roots, we asked whether direct physical root contact plays a role in alloinfection and whether root exudates enhance mycelial growth in soil alone. A rhizobox system was designed to differentiate the effects of each mechanism: a buffer zone created by nylon mesh was used to test the first mechanism, and young carrots with a root system similar to lateral roots were used to test the second. Alloinfections were generated in rhizoboxes via diseased taproots transplanted close to healthy, mature carrots. The nylon mesh had no significant effect on disease intensity (reflecting alloinfection), providing evidence that mycelial growth in soil contributed more to disease spread than did physical contact among roots. Nor did young carrots significantly affect alloinfection; thus root exudates had little effect on mycelial growth.
Plant Pathology, 2007
Cavity spot of carrot (CCS), one of the most important soilborne diseases of this crop worldwide,... more Cavity spot of carrot (CCS), one of the most important soilborne diseases of this crop worldwide, is characterized by small sunken elliptical lesions on the taproot caused by a complex of pathogens belonging to the genus Pythium, notably P. violae. In most soilborne diseases the soil is the source of inoculum for primary infections, with diseased plants then providing inoculum for secondary infections (both auto- and alloinfection). Using fragments of CCS lesions to infest soil, it was demonstrated that CCS lesions on carrot residues can cause primary infection of healthy roots. Using a novel soil infestation method, in which an artificially infected carrot root (the donor plant) was placed close to healthy roots (receptor plants) the formation of typical CCS lesions were induced more efficiently than the use of classical soil inoculum and showed that CCS can spread from root to root by alloinfection from transplanted diseased roots. The method also demonstrated the polycyclic nature of a CCS epidemic caused by P. violae in controlled conditions. Secondary infections caused symptoms and reduced root weight as early as two weeks after transplantation of the diseased carrot. This reproducible method may be used for delayed inoculation and for studying the effect of cropping factors and the efficacy of treatments against primary and secondary cavity spot infections.
The food systems that provide the caloric requirements for most of the world’s population are pla... more The food systems that provide the caloric requirements for most of the world’s population are plant-based, including, rice, wheat and maize. The health and productivity of plant systems is a prerequisite of food security and human health. There are many general threats to plant systems that put plant biosecurity at risk, including global trade of plants and plant products, climate change, population growth and landscape exploitation. Bioterrorism is one more threat to consider when developing a strategy for plant biosecurity. Plant systems are vulnerable to biocrime and bioterrorism. Various lists of threat agents and different approaches to risk assessment have been developed to guide research and policy decisions. Yet an integrated strategy for global plant biosecurity is lacking.
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Papers by Suffert Frédéric