Á. Mesterházy

Genetic variability of central European isolates of the Fusarium graminearum species complex

The main causative agents of Fusarium head blight in central Europe are Fusarium graminearum and F. culmorum. We examined the mycotoxin producing ability, aggressiveness and molecular variability of F. graminearum isolates. Altogether twenty-six Hungarian, three Austrian isolates and representatives of eight species identified in the F. graminearum species complex were involved in this study. Mycotoxin producing abilities of the isolates were tested by GC-MS and HPLC. The central European isolates were found to belong to chemotype I (producing deoxynivalenol). Most isolates produced more 15-acetyl-deoxynivalenol than 3-acetyl-deoxynivalenol suggesting that they belong to chemotype Ib. All F. graminearum isolates were found to be highly pathogenic in in vitro aggressiveness tests. Phylogenetic analysis of random amplified polymorphic DNA profiles, and restriction profiles of the intergenic spacer region of the ribosomal RNA gene cluster of the isolates allowed clustering of the central European isolates into 17 and 16 haplotypes, respectively. When RAPD and IGS-RFLP data were combined, almost every single central European F. graminearum isolate could be differentiated (27/29 haplotypes). Sequence analysis of a putative reductase gene of some isolates was also performed. Based on molecular data, the majority of the central European isolates belonged to F. graminearum sensu stricto characteristic to the northern hemisphere, with the exception of one Hungarian isolate, which was not related to any known species of the F. graminearum species complex based on sequence data. The taxonomic assignment of two other Hungarian isolates, previously suggested as belonging to F. boothii based on mitochondrial DNA restriction profiles, was supported by sequence analysis.

Common resistance to different Fusarium spp. causing Fusarium head blight in wheat

Different sets of wheat genotypes were tested under field conditions by spraying inocula of isolates of seven Fusarium spp. and Microdochium nivale (formerly F. nivale) in the period 1998–2002. The severity of Fusarium head blight (FHB), Fusarium-damaged kernels (FDK), the yield reduction and the deoxynivalenol (DON) contamination were also measured to describe the nature of the resistance. The degrees of FHB severity of genotypes to F. graminearum, F. culmorum, F. avenaceum, F. sporotrichioides, F. poae, F.␣verticillioides, F. sambucinum and M.nivale were very similar, indicating that the resistance to F.␣graminearum was similar to that for other Fusarium spp. listed. This is an important message to breeders as the resistance relates not only to any particular isolate of F. graminearum, but similarly to isolates of other Fusarium spp. This holds true for all the parameters measured. The DON contamination refers only to DON-producers F. graminearum and F. culmorum. Highly significant correlations were found between FHB, FDK, yield loss and DON contamination. Resistance components such as resistance to kernel infection, resistance to DON and tolerance were identified in the more susceptible genotypes. As compared with western European genotypes which produced up to 700xa0mgxa0kg−1 DON, the Hungarian genotypes produced only 100xa0mgxa0kg−1 at a similar FDK level. This research demonstrates the importance of measuring both FDK and DON in the breeding and selection of resistant germplasm and cultivars.

Mycotoxin production and molecular variability of European and American isolates of Fusarium culmorum

The main causative agents of Fusarium head blight are Fusarium graminearum and Fusarium culmorum. We examined the mycotoxin-producing abilities and molecular variability of 37 Fusarium culmorum isolates collected from the Pan-Northern Hemisphere, together with isolates representing related species. Mycotoxin-producing abilities of the isolates were tested by thin layer chromatography and by PCR using primer pairs specific for the Tri7 and Tri13 genes. Thirty isolates belonged to chemotype I (producing deoxynivalenol and 3-acetyl-deoxynivalenol), while seven represented chemotype II (producing nivalenol and/or fusarenone X). The presence of a functional Tri7 gene correlated well with nivalenol production. Isolates belonging to chemotype I were in general more pathogenic in in vitro tests than those belonging to chemotype II. Phylogenetic analysis of the random amplified polymorphic DNA profiles (RAPD) of the isolates enabled the isolates to be clustered into different groups. Most isolates from Hungary exhibited identical RAPD profiles. A similar clustering was found on the tree based on restriction analysis of the intergenic spacer region data. Sequence analysis of a putative reductase gene fragment of the isolates was also carried out. A correlation was detected between the geographic origin of the isolates and their position on the cladogram produced based on sequence data. The presence of mating type gene homologues was also tested with primer pairs specific for MAT1-1 and MAT1-2. The isolates carried either MAT1-1 or MAT1-2 homologues. No correlation was observed between clustering of the isolates based on RAPD, restriction analysis of the intergenic spacer region or sequence data and the distribution of MAT idiomorphs. Similarly, no correlation was detected between mycotoxin-producing abilities or aggressiveness and molecular characteristics of the isolates. Statistical analysis of RAPD data and lack of strict correlation between trees based on different data sets supported the view that Fusarium culmorum has a recombining population structure. The presence of mating type gene homologues in the isolates indicates that the recombining population structure is caused by ongoing or past meiotic exchanges.

ESI-MS and MS/MS identification of the first ceramide analogues of fumonisin B1 mycotoxin from a Fusarium verticillioides culture following RP-HPLC separation.

Following the earlier detection of six new esterified fumonisin B1 (EFB1) isomers containing three acyl groups in a Fusarium verticillioides-inoculated rice culture, it was assumed that linoleic, palmitic or oleic acid esterifies one of the free OH groups on the fumonisin backbone. On the basis of the results of our recent investigations we now propose that these EFB1 isomers are actually 3-O- and 5-O-acyl derivatives of FB1 (3-O-linoleoyl-FB1, 5-O-linoleoyl-FB1, 3-O-palmitoyl-FB1, 5-O-palmitoyl-FB1, 3-O-oleoyl-FB1 and 5-O-oleoyl-FB1). A F. verticillioides strain was identified that produced not only O-acyl-FB1 isomers, but also low amounts of three N-acyl derivatives (N-linoleoyl-FB1, N-palmitoyl-FB1 and N-oleoyl-FB1), which eluted from the HPLC column after the six O-acyl compounds and in the same sequence as for the O-acyl compounds. The characteristic positive and negative ESI-MS/MS spectra obtained after solid-phase extraction of the culture extract facilitated identification of these N-acyl-FB1 derivatives. The biosynthesis of N-palmitoyl-FB1 by F. verticillioides was verified by spiking the culture extract with synthetic N-palmitoyl-FB1. This is the first report of the separation and mass spectrometric identification of the six O-acyl- and three N-acyl-FB1 derivatives extracted from a F. verticillioides culture.

Node infection caused by Fusarium graminearum in wheat.

An undescribed symptom caused by Fusarium graminearum was detected in wheat fields showing masses of orange sporodochia on the node and neighbouring stem tissue. Normally the head above infected nodes dies and only chaff is harvested. This is the first formal description of this type of stem infections caused by F. graminearum. The economic importance of these disease symptoms need further evaluation.

Reduction of deoxynivalenol (DON) contamination by improved fungicide use in wheat. Part 2. Farm scale tests with different nozzle types and updating the integrated approach

Fungicidal control of Fusarium head blight (FHB) of wheat with fungicides generally has poor efficacy (0–40%). However, small plot trials prove that a 70–90% reduction in toxin contamination is possible. We compared two variants of side-spraying nozzles with the Turbo FloodJet. The new nozzle combination (QJ 90, TT F, XR B) reduced visual FHB scores by 50% as compared to the standard TeeJet XR nozzles. The fungicide choice is decisive, the best product reduced DON by 81%, the least effective only by 31%. Greater genetic resistance is also decisive, the most resistant cultivar showed a 73% reduction in DON across all treatments. The combined effect of the fungicide + cultivar was 98.5% between the UTC and best fungicide/variety combination (GK Fény/PT) across three years. The new combined nozzle was more effective at the better fungicides containing prothioconazole, metconazole and tebuconazole, at the less effective fungicides its effect was only average. Correlations between small plot (Part 1) and farm tests were rxa0=xa00.96 (Pxa0=xa00.001) for FHB, rxa0=xa00.91 (Pxa0=xa00–001) for FDK, and rxa0=xa00.75 (Pxa0=xa00.02) for DON indicating that small plot results forecast field usefulness and reduction in field control was close to the small plot results for all traits. The heart of integrated plant management (IPM) is the combination of variety resistance, the effective fungicide and the side-spraying technology with appropriate nozzle choice. Resistance governs fungicide reduction, nozzle influence, effect of previous crop and tillage. Susceptible cultivars should be withdrawn from production, but cultivars such as GK Fény treated with preventive fungicides at the flowering phase can be grown without any serious food safety risk. With a careful field-specific IPM combination, the reduction can be doubled without significant additional costs.

Reduction of deoxynivalenol (DON) contamination by improved fungicide use in wheat. Part 1. Dependence on epidemic severity and resistance level in small plot tests with artificial inoculation.

Fungicide control of FHB of wheat generally has poor efficacy and mostly susceptible cultivars are grown. Therefore, the toxin risk is high. We developed a more efficient control by combining an improved resistance with a more precise evaluation of fungicides. Small plot tests (5m2), along with artificial inoculation were used. Visual head symptoms (FHB), kernel infection (FDK) and DON content were evaluated (2009–2012). Fungicide treatments were preventive at the full flowering stage with four isolates of F. graminearum and F. culmorum. The best fungicide decreased DON by 75% (variation between the four years: 60–93%), the least effective gave a 44% reduction (variation: 30–59%). From medium to very high epidemic severity, smaller differences were observed in reduction (64–68%), but the best reduction was seen at medium disease pressure. The medium susceptible GK Békés reduced DON from 5.86xa0mg/kg to 2.36–3.46xa0mg/kg for the fungicides used. The medium resistant GK-Fény varied for fungicides between 0.86–2.58xa0mg/kg, UTC: 3.90xa0mg/kg), the most susceptible GK-Kalász gave 1.07–5.32xa0mg/kg for fungicides (UTC: 10.01xa0mg/kg). The cumulative effect of fungicide/variety had a 91% reduction across years. The high reduction is not enough the DON content should also be lower than the 1.25xa0mg/kg limit. Correlations between traits for fungicides were between rxa0=xa00.98–0.99 (pxa0<xa00.001), and DON gave the most reliable results. Beside fungicide efficacy, varietal resistance is an important component of effective control of FHB in the field. Susceptible cultivars should be withdrawn from production, but cultivars such as GK Fény can be grown without any serious food safety risk with a single preventive treatment. The fieldwork will be outlined in Part 2.

Reduction of deoxynivalenol (DON) contamination by improved fungicide use in wheat. Part 3. Reduction of Fusarium head blight and influence on quality traits in cultivars with different resistance levels

Earlier published papers analyzed different quality traits indicating only slight changes in quality following Fusarium head blight (FHB) infection and no strong improvement after fungicide application. Therefore, a selection of quality traits were chosen to gain reliable information on these two factors. Three cultivars were tested for three years (2010–2012) with eight fungicides under natural inoculation by maize residue. Quality traits from Zeleny to extensograph parameters were measured from the grain samples. During the 2010 epidemic year extensograph parameters reacted most sensitively to FHB infection, but fungicides only partially restored the damage. The differences between fungicides were also highly significant. Other traits such as grain hardness, 1000 kernel weight, wet gluten and Zeleny value seldom gave significant differences among the treatments. In non-epidemic years the quality traits were also influenced by fungicides, but the variation was much lower, and the treatments caused both significant positive and negative quality changes. The best improvement was found following application of prothioconazole and tebuconazole active molecules to the crop. Improvement of wheat quality was dependent on resistance level and the antifusarium activity of the fungicides. The most informative traits to detect quality losses or measure the improvements were the rheological traits such as the extensograph parameters (e.g.135xa0min Energy) and farinograph dough stability.