Chemical Composition of Fir, Pine and Thyme Essential Oils and Their Effect on Onion (Allium cepa L.) Seed Quality

Botrytis allii and B. cinerea are important seed-transmitted pathogens of onion. The aim of this study was to determine the chemical compositions of fir, pine and thyme essential oils and evaluate their effects on the germination, vigour and health of onion seeds. Gas Chromatography/Mass Spectroscopy was used for the analysis of the oils' chemical compositions. Seed germination, vigour and health tests were performed on untreated seeds and on seeds treated with volatile compounds of the oils applied at a concentration of 0.2 mu L cm(-3) for 6, 12, 24, 48 and 72 h or at a concentration of 0.4 mu L cm(-3) for 3, 6 and 12 h. The main components of fir oil were bornyl acetate (55.5%) and alpha-pinene (15.6%), pine oil contained mostly alpha-pinene (35.5%) and beta-pinene (18.6%), and thymol (34.2%) and p-cymene (26.2%) prevailed in thyme oil. Almost all treatments significantly reduced seed infestation with Alternaria alternata and Fusarium spp., and some effectively controlled Botrytis spp., however, seed health improvement was usually associated with deterioration of seed germination and vigour. Only treatment with fir oil at a concentration of 0.2 mu L cm(-3) for 6 h effectively controlled seed-borne pathogens and positively affected seed germination. Considering the beneficial effect of the oils on seed health, further studies are necessary in order to establish the optimal conditions for onion seed treatment.