Disease control by sulphur induced resistance

As early as the 19th century, Justus von Liebig (1803 – 1873) identifi ed the lack of vitality of soils and non-existent vigour of plants as relevant causes of increased infections of crops by fungal diseases. Organic farming requires alternative strategies for combating pests and diseases. Soil-applied sulphate fertilisation proved to signifi cantly reduce infection rate and severity of crops by fungal diseases. The potential effi cacy of socalled Sulphur Induced Resistance (SIR) expressed as a reduction of the disease index ranged from 5–50% and 17–35% in greenhouse and fi eld experiments, respectively. Metabolic pathways involved in SIR imply, for instance, the synthesis of phytoalexins, glutathione, glucosinolates and the release of sulphur-containing volatiles.