Physiological side effects of fungicides

Besides their main effects (pathogen elimination) fungicides are known to have positive side-effects on plant physiology. Improved yield is the most appreciated and profitable secondary effect and often a result of enhanced stress resistance and delayed leaf senescence, characterized by reduced chlorophyll loss (Grossmann & Retzlaff, 1997), higher protein content and increased biomass. Such effects have been previously detected with strobilurins applied in wheat and barley in our lab (Wu & v. Tiedemann, 2001 & 2002). We strive to detect such effects induced by novel fungicides which have not been introduced into the market yet. The enhanced stress resistance comprises a very broad spectrum of parameters. Stress is often correlated with alterations of the cellular redox status and oxygen metabolism. The visible stress symptoms are often a result of the accumulation of reactive oxygen species. Hence, we focus on enzymatic antioxidative systems (like ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, glutathione reductase, catalase and unspecific peroxidase) and provide several methods to examine alterations of these components. Additionally, we analyse the two most important non-enzymatic detoxifying antioxidants, i.e. glutathione and ascorbate.We also provide techniques to measure hydrogen peroxide, a detectable product of oxygen radical accumulation. More basic parameters which can be analyzed in our lab are chlorophyll content, total protein and the chlorophyll fluorescence (indicating the fitness of photosystems). A second very interesting point is the induction of resistance in plants which can be elicited through various biotic and abiotic stressors. Although biotic inducers are most common, chemicals can function as resistance inducers, as well. The best known and best studied example is acibenzolar-S-methyl (BION). It is our particular interest to analyse fungicidal compounds for similar effects, by using gene expression of PR1 and salicylic acid levels as indicative parameters for ISR. Furthermore, we want to refer our results to stress experiments with detailed adjustable stressors like ozone under controlled conditions. Most experiments are performed with barley and wheat, grown under constant conditions in the greenhouse or in climate chambers. The interaction of these crop plants with pathogens such as Septoria tritici and the performance of the compounds tested, are of interest, too.We also attempt to adapt our methods to other crops and field samples.

References:

• Grossmann K. and G. Retzlaff (1997). Bioregulatory effect of the fungicidal strobilurin kresoxim-methyl in wheat (Triticum aestivum). Pestic. Sci. 50 (1997), pp. 11–20.
• Wu, Y.-X. and A.v. Tiedemann (2001). Physiological effects of azoxystrobin and epoxiconazole on senescence and the oxidative status of wheat. Pesticide Biochemistry & Physiology, 71, 1-10.
• Wu, Y.-X. and A. v. Tiedemann (2002). Impact of fungicides on active oxygen species and antioxidant enzymes in spring barley (Hordeum vulgare L.) exposed to ozone. Environmental Pollution, 116, 37-47.

Investigator(s): Dr. Nadine Riediger, Dr. A. Schützendübel, Dr. Y.-X. Wu

Supervisor: Prof. Andreas von Tiedemann