PCR chemotyping of Fusarium graminearum, F. culmorum and F.cerealis isolated from winter wheat in Wallonia, Belgium

Within the pathogen complex responsible for Fusarium head blight (FHB) are some species that can produce mycotoxins that accumulate in the grains, creating a threat to human and animal health. In Europe, type B trichothecenes, especially deoxynivalenol (DON), are frequently found in grain batches. Most of the genes involved in producing these mycotoxins (TRI genes) are grouped in a 12- gene core cluster (TRI cluster). Fusarium graminearum, F. culmorum and F. cerealis possess this cluster, but the presence or absence of certain TRI genes, as well as their functionality, results in a strain capable of producing either nivalenol (NIV) or deoxynivalenol and a related acetylated derivative (3- or 15-ADON). Because of the different levels of toxicity in these secondary metabolites, it is important to have a better knowledge of the population in Belgium in order to estimate the risk posed by Fusarium species occurring in wheat ears. Two multiplex PCR reactions, targeting the TRI3 and TRI13 genes, were used to differentiate the strains of the three species cited above in terms of the possible chemotypes (NIV, 3-ADON and 15-ADON). In all, 105 single-spore strains of F. graminearum, 90 of F. culmorum and 20 of F. cerealis, isolated from winter wheat, were tested. The three chemotypes were identified in the F. graminearum population, with the vast majority of the strains (93%) being of the 15-ADON chemotype. For F. culmorum, the 3-ADON chemotype was prominent (76.6%) and the rest of the strains were of the NIV chemotype. The 20 tested F. cerealis strains could produce only nivalenol. The different proportions of chemotypes in F. graminearum and F. culmorum and the existence mixed-chemotype populations in the field indicate different specificities of the chemotypes in epidemics

Pathogenicity of Fusarium temperatum and Fusarium subglutinans on maize stalk and ear under artificial inoculation under field conditions

Pathogenicity of Fusarium temperatum, a new species morphologically similar and phylogenetically closely related to F. subglutinans, was observed on stalk and ear of maize (Zea mays L.). In 2010, this species was established in the culture collection of the Maize Research Institute, stored since 2004. Based on interspecies mating compatibility analyses and confirmed with AFLP fingerprint profiles (done by Munaut), two of 20 tested F. subglutinans isolates belonged to the species F. temperatum. These isolates originated from sorghum (Sorghum bicolour (L.) Moench.) grain. In 2011 and 2012, pathogenicity of 20 (2 F. temperatum and 18 F. subglutinans, respectively) and 4 isolates (2 of each F. temperatum F. and F. subglutinans), respectively, was tested on stalk and ear of two maize hybrids. The artificial inoculation of stalk was done by insertion of a Fusarium-inoculated toothpick into the second internode 7 days after silking. Control plants were inoculated with a sterile toothpick. After 6 weeks, disease intensity was evaluated on the stalk longitudinal section by the 0-6 scale (0 - necrosis localised at the inoculation spot; 6 - necrosis spreads to other internodes). Ear inoculation was done with 2-ml spore suspension in silk channels 3-5 days after silking. Control plants were treated with 2 ml sterile water. The disease intensity was assessed on ears immediately prior to harvest, according to the 1-7 scale (1 - no symptoms; 7 - 76-100% infected kernels). There were not statistically significant differences in pathogenicity between isolates of F. temperatum and F. subglutinans, either on stalk or ear. Differences in hybrids responses and symptoms that isolates of fungal species caused on stalks and ears were poorly visible. According to our knowledge, the F. temperaturm occurrence on sorghum seed as well as its pathogenicity on maize ear and stalk are detected for the first time in the world

Distribution of airborne inoculum of Gibberella zeae in Belgium

Fusarium head blight (FHB) is a common fungal disease in winter wheat in Belgium causing yield losses and sanitary problems due to the production of mycotoxins by species associated to the disease. Fusarium graminearum (teleomorph Gibberalle zeae) is one of the important species involved in the species complex causing FHB and is able to produce wind dispersed ascospores by sexual reproduction. In order to analyse the distribution of airborne inoculum of G. zeae along the year and specially between heading and flowering and to understand the role of this inoculum in the infection of the ears, a network of Burkard spore traps was set up in fields in Walloon Region in Belgium during the cultural season 2011-2012. Total DNA from each fragment of spore trap tape corresponding to 1 day sampling was extracted and the quantity of G. zeae was assessed using a real-time polymerase chain reaction (PCR) assay. First results showed the occurrence of G. zeae airborne inoculum between heading and flowering. The relationship between the distribution of airborne inoculum and the prevalence of G. zeae on infected ears collected in fields was studied in order to evaluate if spore traps coupled with real-time PCR can be used to improve the understanding of the epidemiology of FHB, the prediction of this disease and the control strategies

Phylogenetic diversity of and fumonisin gene cluster distribution within Fusarium isolates from wild banana in China

Banana fruit is one of the most important crops and is currently the second most important fruit produced all over the world. Several Fusarium species have been identified as important pre- and post-harvest pathogens of cultivated banana. However, there are no studies that have been conducted to identify Fusarium contaminants on wild banana. The first objective of this work was to study the phylogenetic and genetic diversity of Fusarium isolates from the F. fujikuroi species complex contaminating fruits of wild banana plants growing in two southern Chinese Provinces, Hainan and Yunnan. The second objective was to study the distribution and configuration of the fumonisin gene cluster within these Fusarium species

Evidence for birth-and-death evolution and horizontal transfer of a mycotoxin biosynthetic gene cluster in Fusarium

In fungi, genes required for synthesis of secondary metabolites are often clustered. The FUM gene cluster is required for synthesis of fumonisins, a family of toxic secondary metabolites produced by species in the Fusarium (Gibberella) fujikuroi species complex (FFSC). Fumonisins are a health and agricultural concern because their consumption is epidemiologically associated with cancer and neural tube defects in humans and other animals. Among FFSC species, the FUM cluster is uniform in gene order and orientation, but located in different genomic positions. Phylogenetic analyses indicated discord between species phylogenies and FUM gene-based phylogenies. Subsequent constraint analyses confirmed the discord, and analyses of variation in synonymous sites indicated that cluster divergence predated, in some cases, and postdated, in one case, divergence of lineages of Fusarium in which the cluster occurs. The results are not consistent with the discord resulting from transspecies evolution of ancestral cluster alleles, or with interspecies hybridization, but are consistent with duplication of the cluster within an FFSC ancestor and subsequent loss and sorting of paralogous clusters in a manner consistent with the birth-and-death evolution seen in several multigene families. Although the results are also consistent with horizontal transfer of the cluster, such a model is less parsimonious because it requires multiple transfer events from unknown but related donors to multiple FFSC recipients. However, the analyses do provide strong support for horizontal transfer of the cluster from FFSC to another Fusarium lineage. Thus, despite conservation of gene organization within it, the FusariumFUM cluster has had a complex evolutionary history