Allelopathic effects of aqueous leaf extracts of Helianthus tuberosus L

Jerusalem artichoke (Helianthus tuberosus L.) is a perennial herbaceous species containing allelopathic compounds. In a laboratory study, aqueous extracts of H. tuberosus were obtained by soaking dried leaf tissues in water for 7 h and compared with the adoption of a mechanical homogenizer. A second study was done with extracts at concentrations corresponding to 2.5%, 5%, 10% and 20% w/w of fresh leaves obtained from fresh, dried or frozen leaf tissues. The weeds Echinochloa crus-galli and Chenopodium album were used as indicator species in the first study. Digitaria sanguinalis and Zea mays were also included as indicator species in the second study. The impact of extracts was assessed in terms of total germination, speed of accumulated germination and seedling root and shoot length of the indicator species. Phytotoxic effects were observed both with the adoption of water soaking and with the mechanical homogenizer, with a reduction of total germination greater than 50% and 60% in C. album and E. crus-galli, respectively. In the second study, significant reduction in at least some of the germination indices was observed in all the indicator species, particularly at 20% extract concentration. Only in some cases differences between extracts obtained from fresh, dried or frozen leaf tissues were found. Extracts from dried leaves were generally the most effective in inhibiting germination of E. crus-galli and D. sanguinalis. None of the tested extracts reduced germination and root length of Z. mays. Single comparisons to control and a whole-range assessment performed using WESIA software pointed out that H. tuberosus leaf extracts generally affected more the speed of germination than total germination.