Ferenc Virányi, Rita Bán, Hedvig Komjáti

Plasmopara halstedii, the downy mildew pathogen of sunflower causes severe yield losses worldwide. Control measures, however, either based genetic resistance or on highly selective fungicides, are uncertain. There is a need, therefore, to find out new ways of disease control by using alternative methods, like induced resistance. BION 50 WG (benzothiodiazole), an immune activator has been applied successfully against powdery mildew of cereals.

Our aim was to see whether BION treatment applied to sunflower would prevent or, at least depress downy mildew development and, if so, what happens with the pathogen in BION-treated plants and how such plants respond to fungal infection at cellular level.

Sunflower cultivars and P. halstedii pathotypes were selected to include both compatible and incompatible (susceptible and resistant) interactions, and BION treatment at different rates was made prior to the whole seedling inoculation of sunflower. Evaluation for visual disease symptoms was followed by microscopic examination of excised root/hypocotyl tissues of each treatment.

A significant level of depression in disease symptoms (fungal sporulation, stunting and leaf chlorosis) was detectable in BION-treated and inoculated plants as compared to non-treated and non-inoculated ones. Furthermore, preliminary experiments by using fluorescence microscopy revealed local cell death and secondary cell division at and around infection sites, respectively. This phenomenon resembled those host reactions of genetically resistant genotypes characterised with the so-called HLI-infection, i.e. the infection delimited to the hypocotyl tissues.

This work was supported partly by the research grant OTKA TO38197, entitled "The role of plant activators and resistance inducers in the resistance of sunflower to fungal pathogens".