Tibor Bartók

Influence of Wheat Cultivar, Species of Fusarium, and Isolate Aggressiveness on the Efficacy of Fungicides for Control of Fusarium Head Blight

Attempts to control Fusarium head blight (FHB) with fungicides have been highly variable. Variability is caused by cultivar resistance, fungicide efficacy, fungicide coverage, timing, and pathogen aggressiveness. In this research, fungicides were tested on winter wheat cultivars with different levels of resistance to FHB using different isolates of Fusarium graminearum and F. culmorum to evaluate the role of host resistance and isolate aggressiveness on severity of FHB. Fungicides were applied to groups of wheat heads to provide full coverage. Incidence and severity of FHB was measured by the severity of head symptoms, percentage of Fusarium-damaged kernels (FDK), yield loss, and deoxynivalenol (DON) contamination. Development of FHB was affected by fungicides, cultivars, fungal isolates, and most of the two-way interactions of these variables. Among the fungicides tested, those containing tebuconazole tended to be more effective in reducing FHB. Reduction of disease in susceptible cultivars may not be adequate to produce marketable yields under conditions of high disease pressure. In most cases, if a fungicide reduced FHB visual symptoms, similar decreases were detected in yield loss, DON concentration, and FDK reaction. In 1998, an increase in DON contamination compared with the Fusarium check was observed with azoxystrobin and carbendazim on the more susceptible cultivar. This increase in DON with some fungicide requires additional research. Research to develop more resistant cultivars, better spraying technology, and more effective fungicides is also needed.

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.

Fumonisin contamination and fumonisin producing black Aspergilli in dried vine fruits of different origin.

Aspergillus niger isolates are able to produce fumonisins in high quantities on agar media with a low water activity. Several agricultural products fit this criterion, including dried vine fruits, dates and figs. Data on the occurrence and role of this species in fumonisin contamination of agricultural products with high sugar content are needed to clarify the importance of A. niger in human health. The mycobiota and fumonisin contamination of various dried vine fruit samples collected from different countries were examined to clarify the role of black Aspergilli in fumonisin contamination of such products. All except two of the examined samples were contaminated with black Aspergilli. Species assignment of the isolates was carried out using sequence analysis of part of the calmodulin gene. The range of fumonisin isomers present in the raisins samples, and produced by A. niger isolates collected from dried vine fruits was also examined using reversed-phase high-performance liquid chromatography/electrospray ionization-ion trap mass spectrometry (RP-HPLC/ESI-ITMS). Among the 30 A. niger/A. awamori isolates identified, 20 were found to be able to produce fumonisins (average contamination: 5.16 mg/kg; range: 0.017-19.6 mg/kg). The average fumonisin content of the 7 dried vine fruit samples which were found to be contaminated by potential fumonisin producing black Aspergilli was 7.22 mg/kg (range: 4.55-35.49 mg/kg). The isolates produced several fumonisin isomers also present in the dried vine fruit samples, including fumonisins B(1-4), 3-epi-FB(3), 3-epi-FB(4), iso-FB(1), and two iso-FB(2,3) forms. Fumonisin B(1) was detected for the first time in A. niger cultures. Most of these isomers have previously only been identified in Fusarium species. Our data indicate that A. niger and A. awamori are responsible for fumonisin contamination of dried vine fruits worldwide. The observed levels of contamination are alarming and pose a new threat for food safety.

Detection and characterization of twenty-eight isomers of fumonisin B1 (FB1) mycotoxin in a solid rice culture infected with Fusarium verticillioides by reversed-phase high-performance liquid chromatography/electrospray ionization time-of-flight and ion trap mass spectrometry

Fumonisin mycotoxins which are hazardous to humans and animals were produced in a Fusarium verticillioides-infected solid rice culture. To decrease the possibility of the formation of artifacts, the fumonisins were analysed by reversed-phase high-performance liquid chromatography/electrospray ionization time-of-flight (RP-HPLC/ESI-TOFMS) and ion trap mass spectrometry (RP-HPLC/ESI-ITMS) immediately after the extraction of the culture material, without any further sample clean-up. The fumonisin isomers were separated by using a flat gradient on a special, high-coverage C(18), narrow-bore HPLC column (YMC-Pack Jsphere ODS H80) suggested for the separation of structural isomers by the manufacturer. Exact mass measurements (TOFMS) of the protonated molecules and extraction of the ion chromatogram corresponding to the empirical formula (C(34)H(59)NO(15)) of FB(1) toxins led to the identification of 29 peaks and shoulders, including those of FB(1). The FB(1) toxin and 28 of its isomers were also detected by ITMS after separation with RP-HPLC. The characteristic m/z values of the product ions, including the backbones obtained by ITMS(2), undoubtedly indicated the structures of the FB(1) isomers for 28 peaks and shoulders. In the MS(2) spectra of the protonated molecules of the FB(1) isomers, with some exceptions, 15 characteristic product ions including the hydrocarbon backbone at m/z 299 were observed. The abundance ratio of the cation at m/z 299 ranged up to 5.8%. The relative quantities of the isomers found in the sample extract were expressed as percentages of the FB(1) content (0.001-0.579%). The total amount of the 28 FB(1) isomers was 2.803% of the quantity of FB(1) that is important from the aspect of food and feed safety.

Heterologous expression of astaxanthin biosynthesis genes in Mucor circinelloides

Most Mucor species accumulate β-carotene as the main carotenoid. The crtW and crtZ astaxanthin biosynthesis genes from Agrobacterium aurantiacum were placed under the control of Mucor circinelloides expression signals. Expression vectors containing the bacterial genes were constructed, and PEG-mediated transformations were performed on a selected M. circinelloides strain. Transformants that exhibited altered carotene production were isolated and analyzed. Southern analysis showed that all plasmids behave as autoreplicative elements. Northern analysis detected the actual heterologous transcription products, whereas thin layer chromatography and high-performance liquid chromatography studies revealed the presence of new carotenoid compounds and intermediates among the transformants.

Role of Fungicides, Application of Nozzle Types, and the Resistance Level of Wheat Varieties in the Control of Fusarium Head Blight and Deoxynivalenol

Fungicide application is a key factor in the control of mycotoxin contamination in the harvested wheat grain. However, the practical results are often disappointing. In 2000-2004, 2006-2008 and 2007 and 2008, three experiments were made to test the efficacy of fungicide control on Fusarium Head Blight (FHB) in wheat and to find ways to improve control of the disease and toxin contamination. In a testing system we have used for 20 years, tebuconazole and tebuconazole + prothioconazole fungicides regularly reduced symptoms by about 80% with a correlating reduction in toxin contamination. Averages across the years normally show a correlation of r = 0.90 or higher. The stability differences (measured by the stability index) between the poorest and the best fungicides are about 10 or more times, differing slightly in mycotoxin accumulation, FHB index (severity) and Fusarium damaged kernels (FDK). The weak fungicides, like carbendazim, were effective only when no epidemic occurred or epidemic severity was at a very low level. Similar fungicide effects were seen on wheat cultivars which varied in FHB resistance. In this study, we found three fold differences in susceptibility to FHB between highly susceptible and moderately resistant cultivars when treated with fungicides. In the moderately resistant cultivars, about 50% of the fungicide treatments lowered the DON level below the regulatory limit. In the most susceptible cultivars, all fungicides failed to reduce mycotoxin levels low enough for grain acceptance, in spite of the fact that disease was significantly reduced. The results correlated well with the results of the large-scale field tests of fungicide application at the time of natural infection. The Turbo FloodJet nozzle reduced FHB incidence and DON contamination when compared to the TeeJet XR nozzle. Overall, the data suggest that significant decreases in FHB incidence and deoxynivalenol contamination in field situations are possible with proper fungicide applications. Additionally, small plot tests can be used to evaluate the quality of the field disease and toxin production.

Rigid cinchona conformers in enantioselective catalytic reactions : New cinchona-modified platinum catalysts in the Orito reaction

The use of cinchona alkaloids (cinchonidine, cinchonine, quinine, quinidine, α-isocinchonine, α-isoquinidine, γ-isoquinidine) in the Orito reaction (hydrogenation of ethyl pyruvate and ethyl benzoylformate) strongly supports the structure of the intermediate complex (cinchona alkaloid “anti‐open” conformer–pyruvate 1 : 1 complex); in addition, so far unknown stereochemical conditions have been identified and the utilization of rigid cinchona conformers in the study of asymmetric syntheses have been generalized.

Electrospray ionization mass spectrometry in the heterogeneous catalyzed organic reactions: unknown compounds in the pyruvate hydrogenation

The transformation of cinchonidine was studied in the presence of hydrogen on Pt/alumina by electrospray ionization mass spectrometry using in‐source CID. So far unknown compounds were identified. Further studies on the basis of these new observations may permit to establish a more comprehensive mechanism of enantioselective hydrogenation of α-ketoesters.

Identification of ethyl pyruvate and dihydrocinchonidine adducts by electrospray ionization mass spectrometry

Several ethyl pyruvate and dihydrocinchonidine adducts, formed by non-covalent interactions with alkali cations, have been identified for the first time using electrospray ionization mass and tandem mass spectrometry. This type of adduct may have an important role in asymmetric reactions of pyruvates in the presence of cinchonas.

Prevention of Fusarium mycotoxin contamination by breeding and fungicide application to wheat

The two main possibilities for decreasing toxin contamination were investigated in this paper. In the breeding section, we found that for resistance evaluation the ratio of Fusarium-damaged kernels is more important as this has a closer correlation with the deoxynivalenol (DON) content than the extent of Fusarium head blight (FHB). A high variability was found among lines from the non-Fusarium programme. A 50% decrease of DON contamination could be achieved by a simple and consequent resistance control. The tests with the variety candidates proved the same; therefore, the resistance screening for variety registration is an effective means to stop the spreading of highly susceptible genotypes. The resistance breeding programme showed an even larger DON decrease related to regular susceptible control varieties. Fungicide treatments were generally only weakly effective. However, it was shown that the testing methodology was poor, and with the optimal coverage spraying as much as 90% reduction of DON on small plot tests can be achieved. A farm-scale technology was also developed where the DON reduction as a mean for 3 years was higher than 70%, more than double the regular praxis data. To stabilize this efficacy, we need the most powerful fungicides, a nearly horizontal spraying of heads (like Turbo FloodJet nozzles) that receive the necessary coverage and so enough active ingredient to protect heads and the spraying technology should be kept rigorously. A combination of resistance and fungicide application can reduce DON contamination levels to below the European Union limit of 1.25 mg kg−1 for levels which would otherwise be around 8–10 mg kg−1. We think that this will solve most of the problems.