Institut für Pflanzenschutz in Ackerbau und Grünland
Fusarium head blight, FHB, is a disease of small-grain cereals caused by various Fusarium species and has a major economic impact. Fusarium graminearum and F. culmorum are among the predominant pathogens of FHB. The infestation of cereal crops with Fusarium spp. leads to yield losses and contamination of the grains with toxic metabolites (mycotoxins) that impair food safety. F. culmorum belongs to the F. sambucinum species complex and is able to infect a variety of cereals such as wheat, maize, barley, oats, triticale and rye. Infested material often contains the trichothecene mycotoxins deoxynivalenol (DON) and the derivatives 3-acetyl-deoxynivalenol (3-ADON) and 15-acetyl-deoxynivalenol (15-ADON), nivalenol (NIV) and the derivative fusarenone X (4-acetyl-nivalenol) as well as the resorcylic acid lactone zearalenone (ZEN).During a study of F. graminearum strains on wheat in North America, a new type A trichothecene mycotoxin, NX-2, was discovered. The structure of NX-2 is similar to that of 3-ADON, but it lacks a carbonyl group at C-8. A deacetylated derivative of NX-2, called NX-3, was also discovered. Only recently, these metabolites were also found in an as yet uncharacterised species of the Fusarium sambucinum species complex from South Africa. The first strains of F. graminearum from North America to produce NX toxins did not produce type B trichothecenes under laboratory conditions. The lack of known trichothecenes motivated the studies that led to the discovery of NX toxins. Strains producing NX-2 were originally found only very rarely, but a more recent study estimates that 20% of the F. graminearum population in the USA produces NX-2. In an even more recent study of F. graminearum strains in Canada, producers of NX-2 were identified among strains of F. graminearum classified as chemotype 15-ADON. In contrast to reports that NX-2-producing strains from the USA did not produce DON, NIV or their acetylated derivatives, most strains in their work produced NX-2 simultaneously with 15-ADON.In a study published by the JKI in collaboration with the University of Göttingen, it was shown that most isolates of F. culmorum collected in Europe and Asia can produce NX-2 toxin simultaneously with DON and 3-ADON or NIV. However, this important discovery is limited to production under optimal temperature and nutrient conditions in the laboratory. Information on production on plant material is not yet available. NX toxins are currently not routinely analysed for suspected infections with F. graminearum or F. culmorum.In the Culm-NX project, plants of various cereals (wheat, barley, oats, triticale, maize) are inoculated with two F. culmorum strains that have shown an accumulation of NX toxins in laboratory tests. The isolates were originally derived from naturally infected maize cobs (240.2sp) and stalks (59.6st). The isolates for inoculation are propagated on PDA and oat grains in the laboratory. For inoculation, the spores are applied in a defined concentration using a spray bottle on 3 consecutive dates, 1 day apart, on the ears or in the cobs of the plants. The main trials are carried out in the greenhouse. In addition, there is a one-year field trial in which two wheat varieties are inoculated with spore suspensions of the two isolates. In order to take into account reduced growth of the isolates on the different plant matrices, which may be due to adaptation to a single host species, all samples for mycotoxin analysis are also analysed in advance using qPCR. Through the targeted quantification of fungal DNA, the mycotoxin concentrations can be normalised to the fungal biomass in the samples.The aim of the project is to confirm the production of these toxins in plant material and harvested crops and to derive a risk for food and feed production.
Federal Ministry of Agriculture, Food and Regional Identity
