Is the Eliciting Effect of Stress Metabolites on Pathogenesis in Winter Wheat Linked to the Sulfur Supply?
The effect of a graded sulfur (S) supply to the soil combined with foliar applications of three different defense metabolites (S0, salicylic acid and cysteine) on the infection rate of winter wheat with powdery mildew (Blumeria graminis) was tested in a pot experiment. Spray applications with all three compounds reduced the infection rate in comparison to the control. The strongest effect was obtained expectedly after S0 application due to its well-established fungicidal effect in this host-pathogen relationship. S0 reduced the infection rate by 47% and 67% at maximum when 50 and 100 mg S0 pot−1 were applied, respectively 8 days after application in comparison to the control. In case of salicylic acid (SA) and cysteine the lower dose of 50 mg pot−1 resulted in a stronger reduction of the infection rate than the higher one when the S supply of the crop was low (5 mg S pot−1). Generally, the infection proceeded slower when plants were fully supplied with S though the initial infection rate was higher in these treatments. In case of spray applications with SA and cysteine the combination effect together with soil-applied sulfate never boosted the effect of a single treatment. Only with S0 the strongest reduction in fungal infection was observed when a high soil S supply was combined with a high foliar S0 application. Cysteine and SA trigger pathogen-related response in plants but defense mechanisms were not further enhanced by soil-applied S fertilization in combination with SA and cysteine spray applications, but obviously down-regulated. This suggests feedback regulation between S uptake, S metabolism, infection rate and SA and cysteine concentrations in the plant.
KeywordsSalicylic Acid Infection Rate Powdery Mildew Winter Wheat Foliar Application
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