Allelopathic Effect of Aqueous Extracts from the Leaves of Peppermint (Mentha piperita L.) on Selected Physiological Processes of Common Sunflower (Helianthus annuus L.)

Abstract

In plants cultivation, some species influencing each other in a favorable manner, and others adversely affect the result of the release of physiologically active substances. These substances, called allelopathic compounds are excreted primarily by underground and aboveground plants’ organs or formed during the decomposition of their remains. Allelopathins show the inhibitory or stimulating effects on the processes of seed germination, growth and physiological activity of plants. The aim of the study was to determine the allelopathic effects of aqueous extracts from the peppermint (Mentha × piperita L.) leaves at various concentrations (1, 3, 5, 10, 15%) on seeds germination and the selected physiological processes of common sunflower (Helianthus  annuus L.) seedlings. Seeds were germinated and plants were grown under greenhouse conditions for 30 days. Germination of sunflower seeds was reduced and electrolyte leakage from seedlings increased with increasing concentrations of aqueous extracts of the peppermint leaves. Increasing concentrations of aqueous extracts of peppermint also caused decrease of chlorophyll a and an increase of chlorophyll b content. The highest increase of the maximum photochemical efficiency of photosystem II was observed in H. annuus L. treated with 15% peppermint extract in comparison to the lower concentration of extracts  and to the control. Non-photochemical and photochemical quenching and vitality index of hotosystem II decreased with increasing concentrations of allelopathic substances in peppermint extracts.