Induction of Resistance with Benzothiadiazole in Sunflower: a Comparison of Biotrophic vs. Necrotrophic Pathosystems

In the present work we aimed at comparing the effect of benzothiadiazole (BTH) treatment on defence reactions of sunflower plants to downy mildew and white rot diseases. BTH treatment resulted in reduced disease symptoms in biotrophic and in the early stage of the necrotrophic interactions. To get a better insight into the effect of BTH, changes in the activities of polyphenol oxidase and peroxidase enzymes, as well as the expression of the host response-associated sunflower genes were examined in the plants. Inoculation with Plasmopara halstedii enhanced the polyphenol oxidase and peroxidase enzyme activities, while inoculation with Sclerotinia sclerotiorum did it only at 4 dpi. However, most importantly, in each case extracts from BTH pretreated and inoculated plants showed the highest polyphenol oxidase and peroxidase enzyme activities. Similarly, the accumulation of GST and PDF transcripts was detected following inoculations with both biotrophic and necrotrophic pathogens, and again, BTH pre-treatment enhanced GST and defensine gene activities in the inoculated plants. We suggest that induction of enzyme activities, as well as of the elevated expression of GST, PDF and PR5 genes by BTH pre-treatment may be a significant part of the induced resistance of sunflower to downy mildew and white rot (white mold)