Allelopathic effects of Helianthus tuberosus L. on germination ad seedling growth of several crops and weeds

Helianthus tuberosus L. (Jerusalem artichoke) is a perennial herbaceous species which is cultivated for human and animal consumption and sometimes reported as a dangerous weed in several summer crops. Few reports indicate that this species shows allelopathic behaviour. This study, carried out in laboratory and greenhouse conditions, investigated the effects of aqueous extracts from leaf tissues and powdered dried leaves on total seed germination, speed of germination and shoot and radicle elongation of several annual population species. Aqueous extracts were applied at 2.5, 5, 10 and 20%, to seeds in Petri dishes, and powdered dried leaves were applied at 2 t ha–1 to seeds planted in pots. The crops included in the experiments were maize (Zea mays L.), green bean (Phaseolus vulgaris L.), pea (Pisum sativum L.), rice (Oryza sativa L.), tomato (Lycopersicon esculentum Mill.), winter wheat (Triticum aestivum L.), and zucchini (Cucurbita pepo L. ). Weed species were Amaranthus retloflexus L., Chenopodium album L., Digitaria sanguinalis (L.) Scop., Echinochloa crus-galli (L.) Beauv., Portulaca oleracea L. and Solanum nigrum L. According to their sensitivity, tested species were grouped into negligibly or poorly sensitive, sensitive to high concentrations and sensitive. Species belonging to the first group were maize, green bean, pea, C. album and P. oleracea. Species sensitive to the highest concentrations were rice, winter wheat, D. sanguinalis and S. nigrum. In the last group, which included tomato, zucchini, A. retroflexus and E. crus-galli, total germination of the last three species was reduced by about 49%, on average. S. nigrum showed no germination at 20% extract concentration. In general, speed of germination was affected more than total germination. In some cases, in particular at low concentrations, a stimulatory effect was recorded.