Efeito alelopático de extratos de casca de café em sementes e plantulas Ipomoea Triloba L. e Bidens Pilosa

Abstract

Allelopathy is defined as the beneficial or harmful influence on an individual, plant, or microorganism, mediated by allelochemicals. In plants, such compounds originate from secondary metabolites, released into the environment from different parts of the plant. The aim of this study was to evaluate the allelopathic effect of coffee husk extract on the growth of weed seeds, including bindweed (Ipomoea triloba), Spanish needle (Bidens pilosa), and lettuce (Lactuca sativa), used as a model plant. For this purpose, 9 treatments were used, consisting of four concentrations of extracts 1 (ethanolic) and 2 (aqueous) of coffee husk residues. To obtain extract 1, coffee husks were subjected to the solid-liquid reflux method, and to obtain extract 2, a simple method was considered, in which coffee husks were submerged in water for 24 hours. From extract 1, the following treatments were constructed: T1 (1.538 x 10 -2 g mL -1 ),

T2 (3.077 x 10-2 g mL -1 ), T3 (4.615 x 10-2 g mL -1 ), and T4 (6.154 x 10-2 g mL -1 ) of extract 1

(E1). And T1 (5 x 10 -1 g mL -1 ), T2 (1 x 10 -1 g mL -1 ), T3 (1.5 x 10 -1 g mL -1 ), T4 (2 x 10 -1 g

mL -1 ) of extract 2 (E2), plus T0 (control, only distilled water). To evaluate the growth of seeds subjected to different extracts and concentrations, the following tests were performed: germination test, first germination count, germination speed index, measurement of root and shoot length, and seed imbibition analysis. The experimental design used was completely randomized (CRD), with a factorial (2x4) +1 with a total of 9 treatments from the concentrations of extracts 1 and 2 of coffee husk, with 4 replicates of 25 seeds each. The data were subjected to the ESD (Extreme Studentized Deviate) test to identify outliers. The SPEEDSTAT 2.4 software was used to perform the analysis of variance (p ≤ 0.05), regression, Scott-Knott test, and Dunnet test (comparison of treatments), to generate regression plots of imbibition curves. The results showed that the aqueous extract, at its lowest concentration, significantly promoted the germination of Bidens pilosa seeds, while the ethanolic extract caused inhibition, regardless of concentration. For the species Ipomoea triloba, both extracts caused a reduction in germination with increasing extract concentrations, with the ethanolic extract being the most pronounced. Regarding Lactuca sativa, the ethanolic extract completely inhibited germination, and the aqueous extracts, at higher concentrations, led to a reduction in germination and seed vigor. The seed imbibition results for Bidens pilosa, Ipomoea triloba, and Lactuca sativa showed different behaviors in the imbibition process, with the extracts causing a delay in seed imbibition for the species. It is concluded that the extracts, mainly extract 1 (ethanolic), significantly inhibited the germinative potential and vigor of Spanish needle seeds, while extract 2 showed a peculiar effect of stimulating germination at low concentrations. Both extracts caused a reduction in the germinative potential of bindweed and lettuce. Imbibition patterns indicated a decrease in species absorption capacity with increasing concentration and stabilization for Spanish needle, bindweed, and lettuce.