The biggest problems limiting organic production is the heavy contamination of seeds by phytopathogens, which then spread to plants and cause a reduction in their yield or death. The aim of the research was to develop an innovative technology enabling improvement of seed quality and plant productivity by using beneficial microorganisms and biological agents. The organically produced commercial seeds were treated with whey, Skotan yeast, water suspensions of two consortiums of bacteria, M1 ( Pantoea sp. X58AD and Pseudomonas sp. Ps118AA) or M2 (Enterobacter sp. Pi119AC and Pantoea sp. Pi72ED) isolated from the onion root rhizosphere, commercial microbiological biopreparations (Serenade, Contans, Polyversum, Totalhumus), and hot water (50oC). The organic seeds were strongly infected by saprotrophic and pathogenic fungi. All the seed treatments significantly reduced the occurrence of phytopathogens and increased seed germination kinetics and plant emergence, plant growth and bulb yields, gas exchange, and the index of chlorophyll content in leaves. The single seed treatments with the isolated bacterial consortium exhibited similar (M1) and higher (M2) effectiveness than the commercial preparations, and all of them had greater fungicidal effects than whey and the hydro-thermotherapy. The enrichment of isolated bacterial consortium M2 with whey and Skotan yeast and M1 with Totalhumus increased the fungicidal and growth stimulating effectiveness the most.
