Potencial fitotóxico de extratos de Cajanus cajan (L.) Millsp. na germinação e crescimento de Lactuca sativa L

Abstract

Pigeon pea (Cajanus cajan (L.) Millsp.) is widely used as green manure and cover crop due to its ability to improve the physical and chemical conditions of the soil and suppress weeds. Furthermore, this species can release chemical substances into the environment, known as allelochemicals, which justifies the investigation of their phytotoxic potential. The objective of this research was to evaluate the phytotoxic potential of aqueous extracts of pigeon pea on the germination and growth of Lactuca sativa L. (lettuce), aiming to contribute to more balanced and resilient agricultural systems. Lettuce seeds were used as a bioindicator of the allelopathic potential of pigeon pea, due to their high sensitivity. The experiment was conducted in the Weed Science Laboratory of the State University of Maranhão (UEMA) in a completely randomized design (CRD) with four replications and five treatments, with concentrations of 0, 2.5%, 5.0%, 7.5%, and 10%. The 0% treatment consisted only of distilled water, which served as the control. The aqueous extract was prepared from dried pigeon pea leaves, crushed and macerated in distilled water, and subsequently diluted to obtain concentrations of 2.5%, 5.0%, 7.5%, and 10%. Germination and growth bioassays were performed in Petri dishes under controlled conditions in a 25°C BOD incubator and a 12-hour photoperiod. The variables analyzed were the percentage and speed index of germination (PG and IVG), root length (CR) and shoot length (CPA), fresh root mass (MRF), fresh shoot mass (MPAF), dry root mass (MRS), and dry shoot mass (MPAS). The control showed the highest percentage of germination (100%) compared to the other treatments. The 2.5% extract concentration reduced germination by 83.75%, and from the 5% concentration onwards, no germination occurred. The IVG was higher in the control, followed by the 2.5% concentration (1.23), while no germination occurred at concentrations of 5% or higher. For CPA and CR, the control showed the highest values (1.23) and (0.43), respectively, with these variables being inhibited by the extract concentrations. The control also showed the highest values for MPAF (1.02) and MPAS (1.00), while the other treatments inhibited these variables. Only the control showed an accumulation of MRF (1.001 g) and MRS (1.0006 g), while concentrations from 2.5% to 10% resulted in 0.000 g. It is concluded that extracts of Cajanus cajan (L.) Millsp. have a high phytotoxic potential for germination and seedling growth of Lactuca sativa L., indicating their potential as an alternative in weed management, in line with the principles of agroecology.