Phytotoxic effects of aqueous extracts of sunflower on seed germination and growth of Sinapis alba L., Triticum aestivum L. and Lolium multiflorum Lam.

In petridish and pot culture studies the phytotoxic effects of aqueous extracts of leaves and stems of four sunflower cultivars (‘Oleko’, ‘Tellia’, ‘Sanbro’ and ‘Nutrasol’) were determined on the seed germination and plant growth of ‘Triticum aestivum L., Sinapis alba L. and Lolium multiflorum Lam. In petridish bioassays, the EC50 and EC90 levels showed that stems extracts were more inhibitory to seed germination, radicle and hypocotyl length of S. alba than leaves extracts. There were no significant differences among the sunflower cultivars. Aqueous extracts from leaves and stems of cultivars ‘Tellia’ and ‘Sanbro’ inhibited the seed germination of L. multiflorum but did not affect the seed germination of T. aestivum. In pot culture the EC50 and EC90 levels showed that the stems extracts had highest allelopathic activity than leaves extracts. Both stem and leaves extracts applied at the highest concentration (12.5% w/v) completely suppressed the growth of S. alba and L. multiflorum plant but had little effects on T. aestivum plant growth, especially using ‘Tellia’ extracts. The bioavailability of aqueous extracts in sandy loam soil did not show significant differences among the cultivars and type of extract with average values between leaves and stems aqueous extracts of 25% and 37% for ‘Tellia’ and ‘Sanbro’, respectively.