Priming is one of the most common methods improving quality of seeds. The purpose of the research was to study effects of osmopriming combined with grapefruit extract (Biosept 33 SL) treatment on zinnia seed germination, vigour and infestation with fungi at 10 and 20°C. Two seed samples, cv. Kirke and Orys, varying in initial infestation with Alternaria zinniae, were treated with Biosept 33 SL solutions at concentrations of 0.05, 0.25, 0.5 and 1.0%, during and after priming in polyethylene glycol (PEG 8000). Controls were untreated seeds, seeds treated with fungicide Sarfun T 65 DS and seeds soaked in 0.05, 0.25, 0.5 and 1.0% Biosept 33 SL solution. Priming alone, as well as priming combined with grapefruit extracts treatment, significantly improved total germination and vigour of the seeds. Impact of Biosept 33 SL treatment on seed health varied among samples and was strongly influenced by initial seed infestation with fungi, applied doses of the preparation and temperature of incubation.

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