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

Isolation and characterisation of azoxystrobin degrading bacteria from soil

The first strobilurin fungicides were introduced in 1996, and have since been used in a vast array of disease/plant systems worldwide. The strobilurins now consist of 16 compounds and represent the 2nd most important fungicide group worldwide with 15% of the total fungicide market share. Strobilurins are moderately persistent in soil, and some degradation products (e.g. azoxystrobin acid) have been detected as contaminants of freshwater systems. Little is currently known about the transformation processes involved in the biodegradation of strobilurins or the microbial groups involved. Using sequential soil and liquid culture enrichments, we isolated two bacterial strains which were able to degrade the most widely used strobilurin, azoxystrobin, when supplied as a sole carbon source. 16S rRNA showed that the strains showed homology to Cupriavidus sp. and Rhodanobacter sp. Both isolated strains were also able to degrade the related strobilurin compounds trifloxystrobin, pyraclostrobin, and kresoxim-methyl. An additional nitrogen source was required for degradation to occur, but the addition of a further carbon source reduced compound degradation by approximately 50%. However, (14)C radiometric analysis showed that full mineralisation of azosxystrobin to (14)CO2 was negligible for both isolates. 16S rRNA T-RFLP analysis using both DNA and RNA extracts showed that degradation of azoxystrobin in soil was associated with shifts in bacterial community structure. However, the phylotypes which proliferated during degradation could not be attributed to the isolated degraders

Influence of temperature on infection, growth, and mycotoxin production by Fusarium langsethiae and F. sporotrichioides in durum wheat

Information concerning the temperature requirements of the species causing Fusarium head blight of small grains is essential for understanding which species cause the disease in different areas and years, for developing weather-driven disease models and for predicting mycotoxin type and quantity in kernels. The optimal temperature range for growth was 20-25 \ub0C for Fusarium langsethiae and 25-30 \ub0C for F. sporotrichioides, and the optimum for production of both T-2 and HT-2 toxins was 15 \ub0C for F. langsethiae and 10-15 \ub0C for F. sporotrichioides. Floret infection occurred from 10 to 40 \ub0C for F. sporotrichioides (69.8% average incidence of infected florets) and from 10 to 35 \ub0C for F. langsethiae (17.6% of infected florets). The optimal temperature for spike colonisation was 25 \ub0C for F. langsethiae and 30 \ub0C for F. sporotrichioides, and the optimal temperature range for mycotoxin production was 15-35 \ub0C for F. langsethiae and 20-25 \ub0C for F. sporotrichioides. The quantity of fungal DNA in inoculated spikes was 5.5-times greater for F. sporotrichioides than for F. langsethiae; F. langsethiae DNA was first detected 2 days post-inoculation (dpi), and F. sporotrichioides DNA was first detected 4 dpi. Toxins were first detected 4 and 2 dpi for F. langsethiae and F. sporotrichioides, respectively