azoxystrobin and fenpropimorph

The two fungicides azoxystrobin and fenpropimorph are used against powdery mildew and rust diseases in wheat (Triticum aestivumL). Azoxystrobin, a strobilurin, inhibits fungal mitochondrial respiration and fenpropimorph, a morpholin, represses biosynthesis of ergosterol, the major sterol of fungal membranes. Although the fungitoxic activity of these compounds is well understood, their effects on plant metabolism remain unclear. In contrast to the fungicides which directly affect pathogen metabolism, benzo(1,2,3) thiadiazole-7-carbothioic acid S-methylester (BTH) induces resistance against wheat pathogens by the activation of systemic acquired resistance in the host plant. In this study, we monitored gene expression in spring wheat after treatment with each of these agrochemicals in a greenhouse trial using a microarray containing 600 barley cDNA clones. Defence-related genes were strongly induced after treatment with BTH, confirming the activation of a similar set of genes as in dicot plants following salicylic acid treatment. A similar gene expression pattern was observed after treatment with fenpropimorph and some defence-related genes were induced by azoxystrobin, demonstrating that these fungicides also activate a defence reaction. However, less intense responses were triggered than with BTH. The same experiments performed under field conditions gave dramatically different results. No gene showed differential expression after treatment and defence genes were already expressed at a high level before application of the agrochemicals. These differences in the expression patterns between the two environments demonstrate the importance of plant growth conditions for testing the impact of agrochemicals on plant metabolism.

Topics: Acrylates; Antifungal Agents; Fungi; Fungicides, Industrial; Gene Expression Profiling; Gene Expression Regulation, Plant; Gene Library; Methacrylates; Morpholines; Oligonucleotide Array Sequence Analysis; Plant Diseases; Pyrimidines; RNA, Plant; Strobilurins; Thiadiazoles; Triticum

Strobilurin fungicides have a broad spectrum activity against all major foliar pathogens of wheat. In addition to this extraordinary fungicidal activity side-effects have been reported which result in higher yields of cereals, e.g. the reduction of respiration, delayed leaf senescence, activation of nitrogen metabolism as well as increased tolerance against abiotic stress factors. In the vegetation period 2000/2001 field trials were carried out at three sites in North Rhine-Westphalia to study the effects of three strobilurin fungicides on the yield formation of six winter wheat varieties. The strobilurins were applied two times as the commercial products Stratego (trifloxystrobin + propiconazole), Amistar/Pronto Plus (azoxystrobin/spiroxamine + tebuconazole) and Juwel Top (kresoxim-methyl + epoxiconazole + fenpropimorph. Fungicide-treated plants were kept disease-free by an initial azole-application in GS 31 in order to exclude disease effects on physiological parameters relevant to yield formation. Photosynthetic electron transport of strobilurin-treated wheat, was improved as early as at GS 65 compared to azole-treated plants. Differences often increased with growth stage and were closely related to a delay in leaf senescence. A higher photosynthetic activity of strobilurin-treated plants was confirmed by gas exchange and chlorophyll fluorescence measurements under field conditions. The yield benefit of wheat from strobilurin treatments varied from 2% to 9% depending on an improved photosynthetic capacity due to a higher and/or prolonged activity. Neither yield potential nor disease susceptibility of the cultivar had an effect on the height of the extra yield which, in contrast was modified by location and wheat genotype.

Topics: Acetates; Acrylates; Azoles; Chlorophyll; Epoxy Compounds; Fungicides, Industrial; Germany; Imines; Methacrylates; Morpholines; Phenylacetates; Photosynthesis; Pyrimidines; Strobilurins; Triazoles; Triticum