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

Mapping of FHB resistance QTLs in the Mini Mano/Frontana and Frontana/Remus DH populations

Fusarium head blight (FHB) is a devastating disease of wheat ( Triticum aestivum L.) world-wide. The objective of this study was to identify FHB resistance QTLs of the Brazilian spring wheat cultivar Frontana through molecular mapping. Frontana has small and medium effective QTLs. These types of QTLs are sensitive for the environmental factors and for the problems of heterogeneity. 206 DH lines from Frontana/Remus (IFA-Tulln) /2005–2006/ and 105 DH lines of Mini Mano/Frontana (CRC Szeged) /2006–2007/ were inoculated with isolates of F. graminearum and F. culmorum . The Frontana/Remus DH population had wide differences in flowering time and plant height. MM/Frontana was created by CRC, Szeged so that too early and late DH lines were discarded and the remaining lines flowered within five days. Lines with extra plant height were also discarded, so differences were kept within 20–30 cm. In the Frontana/Remus population QTLs were identified on the chromosomes 3B, 5A, 6B. In the MM/Frontana population chromosomes 3B and 5B gave positive signal. Although in both populations Frontana was the resistant parent no QTL markers were identical for them. It seems that the more homogeneous population increases the accuracy of the QTL analysis. An increased morphological homogeneity seems to be necessary to decrease „background noise“ in QTL analyses and increase precision. Until now no QTL were found that gave positive signs for all epidemic situations. As QTLs are not validated, it is early to apply MAS in breeding

Reproductive mode of central European Fusarium graminearum and F. culmorum populations

Fusarium head blight caused mainly by Fusarium graminearum and F. culmorum is the most important disease of wheat in Central Europe. While F. graminearum is homothallic, no sexual cycle has been observed in F. culmorum . Knowledge regarding the species distribution and population structure of these pathogens is important to estimate their significance for breeding. There are two fundamental means by which fungi and other organisms transmit genes to the next generation: through clonal reproduction or by sexual recombination. To clarify the population structures of F. culmorum and F. graminearum in Central Europe, RAPD and IGS-RFLP data sets of the isolates were subjected to both the index of association tests and tree length tests. Our data indicate that the world-wide F. graminearum and F. culmorum populations have recombining structures, while both the Hungarian F. culmorum and F. graminearum populations reproduce clonally. The frequent occurrence of F. graminearum perithecia on corn residues indicates that this species undergoes a sexual cycle. Both mating type genes have been identified in each examined F. graminearum isolate, while the heterothallic distribution of mating type genes in F. culmorum indicates that this species lost its sexual cycle relatively recently

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 r = 0.96 (P = 0.001) for FHB, r = 0.91 (P = 0–001) for FDK, and r = 0.75 (P = 0.02) 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