Identification and pathogenicity of Alternaria species associated with leaf blotch disease and premature defoliation in French apple orchards

Leaf blotch caused by Alternaria spp. is a common disease in apple-producing regions. The disease is usually associated with one phylogenetic species and one species complex, Alternaria alternata and the Alternaria arborescens species complex (A. arborescens SC), respectively. Both taxa may include the Alternaria apple pathotype, a quarantine or regulated pathogen in several countries. The apple pathotype is characterized by the production of a host-selective toxin (HST) which is involved in pathogenicity towards the apple. A cluster of genes located on conditionally dispensable chromosomes (CDCs) is involved in the production of this HST (namely AMT in the case of the apple pathotype). Since 2016, leaf blotch and premature tree defoliation attributed to Alternaria spp. have been observed in apple-producing regions of central and south-eastern France. Our study aimed to identify the Alternaria species involved in apple tree defoliation and assess the presence of the apple pathotype in French orchards. From 2016 to 2018, 166 isolates were collected and identified by multi-locus sequence typing (MLST). This analysis revealed that all these French isolates belonged to either the A. arborescens SC or A. alternata. Specific PCR detection targeting three genes located on the CDC did not indicate the presence of the apple pathotype in France. Pathogenicity was assessed under laboratory conditions on detached leaves of Golden Delicious and Gala apple cultivars for a representative subset of 28 Alternaria isolates. All the tested isolates were pathogenic on detached leaves of cultivars Golden Delicious and Gala, but no differences were observed between the pathogenicity levels of A. arborescens SC and A. alternata. However, the results of our pathogenicity test suggest that cultivar Golden Delicious is more susceptible than Gala to Alternaria leaf blotch. Implications in the detection of the Alternaria apple pathotype and the taxonomic assignment of Alternaria isolates involved in Alternaria leaf blotch are discussed

A European Database of Fusarium graminearum and F. culmorum Trichothecene Genotypes

. Fusarium species, particularly Fusarium graminearum and F culmorum, are the main cause of trichothecene type B contamination in cereals. Data on the distribution of Fusarium trichothecene genotypes in cereals in Europe are scattered in time and space. Furthermore, a common core set of related variables (sampling method, host cultivar, previous crop, etc.) that would allow more effective analysis of factors influencing the spatial and temporal population distribution, is lacking. Consequently, based on the available data, it is difficult to identify factors influencing chemotype distribution and spread at the European level. Here we describe the results of a collaborative integrated work which aims (1) to characterize the trichothecene genotypes of strains from three Fusarium species, collected over the period 2000-2013 and (2) to enhance the standardization of epidemiological data collection. Information on host plant, country of origin, sampling location, year of sampling and previous crop of 1147 F graminearurn, 479 F culmorum, and 3 F cortaderiae strains obtained from 17 European countries was compiled and a map of trichothecene type B genotype distribution was plotted for each species. All information on the strains was collected in a freely accessible and updatable database (www.catalogueeu.luxmcc.lu), which will serve as a starting point for epidemiological analysis of potential spatial and temporal trichothecene genotype shifts in Europe. The analysis of the currently available European dataset showed that in F. grarninearum, the predominant genotype was 15-acetyldeoxynivalenol (15-ADON) (82.9%), followed by 3-acetyldeoxynivalenol (3-ADON) (13.6%), and nivalenol (NIV) (3.5%). In F culmorum, the prevalent genotype was 3-ADON (59.9%), while the NIV genotype accounted for the remaining 40.1%. Both, geographical and temporal patterns of trichothecene genotypes distribution were identified.</p

A European Database of Fusarium graminearum and F-culmorum Trichothecene Genotypes

Fusarium species, particularly Fusarium graminearum and F culmorum, are the main cause of trichothecene type B contamination in cereals. Data on the distribution of Fusarium trichothecene genotypes in cereals in Europe are scattered in time and space. Furthermore, a common core set of related variables (sampling method, host cultivar, previous crop, etc.) that would allow more effective analysis of factors influencing the spatial and temporal population distribution, is lacking. Consequently, based on the available data, it is difficult to identify factors influencing chemotype distribution and spread at the European level. Here we describe the results of a collaborative integrated work which aims (1) to characterize the trichothecene genotypes of strains from three Fusarium species, collected over the period 2000-2013 and (2) to enhance the standardization of epidemiological data collection. Information on host plant, country of origin, sampling location, year of sampling and previous crop of 1147 F graminearurn, 479 F culmorum, and 3 F cortaderiae strains obtained from 17 European countries was compiled and a map of trichothecene type B genotype distribution was plotted for each species. All information on the strains was collected in a freely accessible and updatable database (www.catalogueeu.luxmcc.lu), which will serve as a starting point for epidemiological analysis of potential spatial and temporal trichothecene genotype shifts in Europe. The analysis of the currently available European dataset showed that in F. grarninearum, the predominant genotype was 15-acetyldeoxynivalenol (15-ADON) (82.9%), followed by 3-acetyldeoxynivalenol (3-ADON) (13.6%), and nivalenol (NIV) (3.5%). In F culmorum, the prevalent genotype was 3-ADON (59.9%), while the NIV genotype accounted for the remaining 40.1%. Both, geographical and temporal patterns of trichothecene genotypes distribution were identified

Etude de l'effet de composés du grain de blé dur sur la régulation de la voie de biosynthèse des trichothécènes B : purification de composés inhibiteurs, analyse des mécanismes impliqués

La résistance à l’accumulation de mycotoxines de Fusarium chez certaines variétés de blé dur résulte de mécanismes naturels, en particulier, des composés endogènes du grain pourraient limiter l’accumulation des trichothécènes par une inhibition de leur biosynthèse. Dans ce contexte, l’objectif principal de cette étude est de rechercher des composés du blé dur inhibiteurs de la toxinogenèse, d’étudier leurs effets et les mécanismes de régulation mis en jeu. Des conditions expérimentales permettant d’étudier in vitro l’effet &quote;anti mycotoxines&quote; de composés à tester ont été mises au point. Ceci a permis de montrer l’efficacité de certains acides phénoliques présents dans les sons de blé pour inhiber la production de trichothécènes. Considérés de façon isolée ou en mélange, les acides phénoliques dérivés de l’acide cinnamique, à des concentrations proches des valeurs physiologiques, limitent l’accumulation de toxines par Fusarium culmorum. Dans un extrait naturel d’acides phénoliques de blé, la présence d’oligomères d’acide férulique augmente fortement l’efficacité inhibitrice. L’inhibition de la production de toxines par ces acides phénoliques s’explique par la forte régulation au niveau transcriptionnel de l’expression de certains gènes de la voie de biosynthèse des trichothécènes. La recherche dans les sons de blé de composés inhibiteurs par une démarche sans à priori sur leur nature a permis la purification d’un dimère d’acide phénolique ayant une activité &quote;anti mycotoxines&quote; près de dix fois supérieure à celle des formes monomériques. Les dimères d’acide phénolique pourraient ainsi constituer des facteurs clés de résistance à l’accumulation de mycotoxines. Plus généralement, les variations de contenu et de disponibilité en acides phénoliques selon les variétés contribueraient aux différences de sensibilité à l’accumulation de mycotoxines chez le blé dur.Resistance to Fusarium mycotoxins accumulation in some varieties of durum wheat results from natural mechanisms; particularly some specific compounds present in https://oskar-bordeaux.fr/admin/item?administrative-continue=481c4615481b26520a455f893e576c7d6f331b78&view_itemkernels could limit trichothecenes accumulation by inhibiting their biosynthesis. The aim of this study is to seek for biochemical compounds from wheat kernels inhibiting mycotoxins biosynthesis, to study their effects and to analyse the regulation involved. Adapted experimental conditions were first developed allowing to study in vitro the &quote;anti-mycotoxin&quote; effect of candidate compounds. Some phenolic acids contained in wheat bran were shown to efficiently inhibit trichothecenes biosynthesis. When tested individually or in mixture, phenolic acids derived from cinnamic acid, at physiological concentrations, limit toxin accumulation by Fusarium culmorum. In a natural extract of phenolic acids, the occurrence of ferulic acids oligomers strongly increases the efficiency of inhibition. The inhibition of toxin production by these phenolic acids is explained by the strong transcriptional regulation of expression of some genes involved in the trichothecenes biosynthesis pathway. A fractionation of wheat bran extracts allowed purification of a phenolic acids dimer exhibiting an &quote;anti-mycotoxin&quote; effect close to ten times more effective than monomeric forms. Dimers of phenolic acids could constitute key resistance factors to mycotoxins accumulation. More generally, variations in phenolic acids content and availability among cultivars may contribute in differences in the levels of mycotoxins accumulation observed in durum wheat

Fusarium temperatum isolated from maize in France

The presence of Fusarium temperatum in France was investigated by analyzing 40 Fusarium strains, previously isolated from infected maize ears in 2011 and formerly identified as Fusarium subglutinans based on morphological characteristics. In this study, 26 strains out of the 40 were identified as F. temperatum and 14 as F. subglutinans based on sequencing of the translation elongation factor 1α gene. The phylogenetic analysis showed that the two species represented two clades strongly supported by bootstrap values. The pathogenicity of F. temperatum strains was confirmed on maize ears. This study provides new information about F. temperatum isolated from maize in France

Caractérisation de l’activité antifongique de biomolécules d’origine végétale sur les champignons mycotoxinogènes Aspergillus westerdijkiae et Fusarium graminearum

National audienc

Cinnamic-derived acids significantly affect Fusarium graminearum growth and in vitro synthesis of type B trichothecenes

International audienceThe impact of five phenolic acids (ferulic, coumaric, caffeic, syringic and p-hydroxybenzoic acids) on fungal growth and type B trichothecene production by four strains of Fusarium graminearum was investigated. All five phenolic acids inhibited growth, but the degree of inhibition varied between strains. Our results suggested that the more lipophilic phenolic acids are, the higher is the effect they have on growth. Toxin accumulation in phenolic acid-supplemented liquid GYEP cultures was enhanced in the presence of ferulic and coumaric acids but was reduced in the presence of p-hydroxybenzoic acid. This modulation was shown to correlate with a regulation of TRI5 transcription. In this study, addition of phenolic acids with greater antioxidant properties resulted in a higher toxin accumulation indicating the modulation of toxin accumulation may be linked to the antioxidant properties of the phenolic acids. These data suggest that, in planta, different compositions in phenolic acids of kernels from various cultivars may reflect different degrees of sensitiveness to “mycotoxinogenesis”

A sensitive real-time PCR assay for the detection of the two Melampsora medusae formae speciales on infected poplar leaves

Melampsora medusae is a quarantine fungus in the European Union (EU) that causes a damaging leaf rust disease on poplars. Two formae speciales of the pathogen can be distinguished, M. medusae f. sp. deltoidae and M. medusae f. sp. tremuloidae, but the EU plant health directive 2000/29/EC currently in force does not make the distinction between them. EU countries must have the ability to detect and identify rapidly the introduction of these quarantine fungi and to conduct extensive surveys in case of outbreaks. Efficient detection tools are thus needed. In this study, a sensitive real-time PCR assay was developed to detect the presence of M. medusae in poplar leaf samples. A unique primer/hydrolysis probe combination targeting both formae speciales was designed using species-specific polymorphisms observed within the internal transcribed spacer region. An additional primer/hydrolysis probe combination was designed from a region of the 28S rDNA that is highly conserved in the genus Melampsora and used in a separate real-time PCR assay in order to check the quality of the DNA extracted from Melampsora urediniospores. The test developed demonstrated a high sensitivity since it enables the reproducible detection of two M. medusae urediniospore in a mixture of 2 mg of urediniospores (ca 800 000 urediniospores) of other Melampsora species. This new real-time PCR tool should be useful for laboratories in charge of official analyses since it has many advantages over the techniques currently used to monitor this quarantine pathogen in Europe

Sanitation of a South African forestry nursery contaminated with Fusarium circinatum using hydrogen peroxide at specific oxidation reduction potentials

Pitch canker, caused by Fusarium circinatum, was first reported in a forestry nursery in the Mpumalanga Province of South Africa in 1990, and it has since spread to almost all forestry nurseries in the country, where it causes significant economic losses. The aim of the current study was to (i) identify sources of F. circinatum contamination in the Karatara forestry nursery in the Western Cape Province and (ii) manage the disease by implementing an oxidation reduction potential (ORP)-based sanitation method using hydrogen peroxide. The irrigation water, planting tray inserts and seeds were screened for fungal contamination. Fusarium circinatum colonies were identified morphologically and confirmed by polymerase chain reaction using speciesspecific primers. Both the irrigation water and planting tray inserts served as sources of inoculum that introduced the pathogen into the nursery. The irrigation water was amended with hydrogen peroxide at an ORP level of 400 mV for an exposure time of 6 h because it was observed that such a treatment effectively killed all F. circinatum spores and was not phytotoxic to pine seedlings under laboratory conditions. In addition, the contaminated planting tray inserts were cleaned in water amended with hydrogen peroxide at an ORP value of 360 mV for 6 h, which was shown to efficiently eliminate all inoculum from planting tray inserts. Since the introduction of the ORP-based sanitation method at Karatara nursery, losses of pine seedlings were reduced to insignificant levels, and field losses were minimized.http://apsjournals.apsnet.org/loi/pdishb2016Microbiology and Plant Patholog