Phytotoxicity of aqueous extracts of Ilex paraguariensis A. St-Hil. leaves on Lolium multiflorum Lam.

Lolium multiflorum Lam. (ryegrass, or azevém in Portuguese) is a grass used as forage and cover crop in vineyards of the southern region of Brazil. However, it has become invasive, with some biotypes identified as resistant to glyphosate. Its control is performed with herbicides, prior to flowering. Aside from plant resistance and damage to the ecosystem and to the population’s health, these herbicides might cause lesions to plant tissues, and change photosynthesis and fruit matu­ration, as already observed in vineyards. Due to the presence of bioactive substances with phytotoxic activity, extracts of native plants might be exploited to develop natural prod­ucts with herbicidal activity. The present study evaluated the effects of aqueous extracts by decoction and infusion of Ilex paraguariensis A. St.-Hil. leaves on germination, seedling for­mation, growth, and on the chlorophyll and tissues of adult L. multiflorum plants. In vitro bioassays were performed at the concentrations of 0% (control - only purified water), 0.5%, 1%, and 2%, comprised of five replicates of 20 L. multiflorum caryopses. Germination percentage, average germination time, average seedling formation time, average seedling length, and dry mass were calculated. Adult L. multiflorum plants were submitted to treatments using extracts by decoc­tion in the concentration of 3% and 5% (and control - only purified water), and chlorophyll content, dry mass, and anatomical cuts were evaluated. Chemical compounds present in the extracts were identified through High-performance liquid chromatography (HPLC). Data were submitted to a unidirec­tional analysis of variance (ANOVA) and a polynomial regres­sion analysis (p < 0.05). Both extracts showed phytotoxic activity, yet the decoction extract had higher phytotoxicity, especially at the concentrations of 1% and 2%, reducing ger­mination percentage and speed, as well as seedling forma­tion and growth. Damage was lower in adult plants, although there was rupture of epidermal cells and chlorophyll parenchyma, as well as plasmolysis at 3 and 6% of the extract. The chemical profile of I. paraguariensis is consistent with the biological activity observed. The hypothesis that the aqueous extract by decoction of I. paraguariensis leaves has potential to develop a natural product with herbicidal activity against L. multiflorum, to be used in vineyards, was confirmed. However, further studies are required to evaluate extract application methodology, individual action of each compound present, and their action mechanisms.