Potencial alelopático de espécies nativas na germinação e crescimento inicial de Lactuca sativa L. (Asteraceae) Allelopathic potential of native species in Lactuca sativa L. (Asteraceae) germination and initial growth

A alelopatia caracteriza-se pelos efeitos danosos ou benéficos sobre o desenvolvimento da vegetação, causados por substâncias químicas produzidas e liberadas para o ambiente por uma planta. Com o objetivo de avaliar o potencial alelopático de espécies brasileiras, foram testados extratos foliares de Cecropia pachystachya Trec. (Urticaceae), Peltophorum dubium (Spreng.) Taub. (Fabaceae), Psychotria leiocarpa Cham. & Schltdl (Rubiaceae), Sapium glandulatum (Vell.) Pax (Euphorbiaceae) e Sorocea bonplandii (Baill.) Burg., Lanj. & Boer (Moraceae), utilizando-se bioensaios de germinação e crescimento e alface (Lactuca sativa L.) como planta alvo. Nesses bioensaios, foram usados extratos foliares aquosos nas concentrações de 2 e 4%, preparados por maceração estática com água fria e quente. Os extratos das cinco espécies causaram atraso na germinação dos aquênios da alface, bem como efeitos tóxicos no crescimento das plântulas, com redução e enfraquecimento das raízes. Os resultados obtidos mostraram a presença de substâncias químicas inibidoras nos extratos, revelando potencial alelopático para as cinco espécies avaliadas.<br>Allelopathy is characterized by harmful or beneficial effects on vegetation development, caused by chemical substances produced and released into the environment by the plant. Aiming to assess the allelopathic potential of Brazilian species, aqueous leaf extracts of Cecropia pachystachya Trec. (Urticaceae), Peltophorum dubium (Spreng.) Taub. (Fabaceae), Psychotria leiocarpa Cham. & Schltdl (Rubiaceae), Sapium glandulatum (Vell.) Pax (Euphorbiaceae), and Sorocea bonplandii (Baill.) Burger, Lanj. & Boer (Moraceae) were tested on lettuce using germination and growth bioassays. In these bioassays, aqueous leaf extracts were used at concentrations of 2 and 4%, prepared by static maceration with cold and hot water. The five species extracts delayed lettuce germination and produced toxic effects on seedling growth, with root reduction and debility. The results point to the presence of inhibitorychemical substances in the extracts, indicating an allelopathic potential for the five species evaluated

Allelopathic growth inhibition and colony formation of the green alga Scenedesmus obliquus by the aquatic macrophytes Stratiotes aloides

Laboratory experiments were conducted to elucidate the allelopathic effects of exudates from the aquatic macrophyte Stratiotes aloides on the growth and morphology of the green alga Scenedesmus obliquus. Both water originating from a S. aloides culture and water that had not been in contact with S. aloides was simultaneously inoculated with S. obliquus cells. In all experiments we observed a highly significant inhibitory effect of Stratiotes water on the green alga. The duration of the lag phase as well as the initial biovolume doubling time of S. obliquus were extended. The growth rate of S. obliquus was only significantly inhibited by the younger Stratiotes plants. Furthermore, the mean particle volume (MPV) of Scenedesmus increased significantly in the presence of Stratiotes water in all three experiments. Microscopic analyses confirmed that S. obliquus forms more colonies in the presence of water from a S. aloides culture. Colonies of phytoplankton have higher sinking rates than single phytoplankton cells of the same species and disappear faster from the upper water layers, reducing the competition for light between algae and macrophytes. [KEYWORDS: Colony formation ; Growth inhibition ; Infochemical ; Macrophytes ; Sedimentation]