Organic acids are known for their antibacterial and antifungal properties. The purpose of the research was to study the effect of acetic, ascorbic, citric and lactic acid treatments on zinnia seed germination, vigour and infestation with fungi. Two seed samples, cultivars ‘Jowita’ and ‘Scarlet Flame’, varying in fungi occurrence intensity, were treated with organic acids solutions at concentrations of 1.0, 2.5 and 5.0%. Controls were untreated seeds, seeds treated with fungicide Penncozeb 80 WP, and seeds soaked for 30 min in distilled water. Acetic acid in the highest extent limited fungal occurrence on seeds, however negatively affected seed germination and vigour. Ascorbic and citric acids had no effect on the total seed infestation with fungi. Moreover, the acids significantly stimulated growth of Botrytis cinerea on the seeds. Lactic acid decreased the number of seeds infected with fungi, especially with Alternaria zinniae and Fusarium spp., however at the highest concentration negatively affected germination parameters and deteriorated seed vigour.

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