Allelopathic potential and phytochemical screening of Piper divaricatum extracts on germination and growth of indicator plant (Lactuca sativa)

Abstract Weeds are one of the most damaging crop pests with estimated annual global damage of around U$ 40 billion. About four million tonnes of pesticide are applied to crops worldwide each year. Currently, there is a growing demand for the use of natural products in agriculture in order to ensure the health of plants and environment. This trend has stimulated research on biodefensives from plant origin. Here, the phytotoxicity of organic extracts and fractions from Piper divaricatum leaves was evaluated on inhibition of emergence and initial growth in lettuce (Lactuca sativa) seedlings. Bioassays were carried out in chamber growth and the detection of compounds classes was performed by Thin Layer Chromatography. Hexane extract completely inhibited emergence and seedling growth at 7.5 and 10.0 mg/mL. Ethanol/methanol extract was highly toxic to seedlings in all concentrations, displaying 100% of inhibition on emergence. Aqueous and alcoholic extracts were submitted to partition and fractions assayed at 2.5 mg/mL. Chloroform fraction of aqueous extract displayed a higher inhibition rate on emergence (100%), however, the fractions obtained from Ethanol/Methanol extract displayed a range of inhibition rate from 33 to 71%, which drastically affected the root and seedling growth. Phytochemical screening using thin layer chromatography combined with chemical revelators was applied. Alkaloids and coumarins were found in chloroform fraction of aqueous extract, both reported as potent inhibitors of emergence, causing changes in cell division, tissue damage, and interfering in cellular transport. Other compounds such as fatty acids and anthracene derivatives were also found in Methanol/Ethanol extract fractions and are reporting for the first time as potential allelochemicals in P. divaricatum.