Assessment of Allelopathic Activity of Arachis Pintoi Krapov. & WC Greg As a Potential Source of Natural Herbicide for Paddy Rice

Pinto peanut (Arachis pintoi Krapov. & W.C. Greg.) is an herbaceous perennial plant which belongs to the Leguminosae family. This plant is well known for its use as a cover crop, but little information is available on the allelopathic potential of this legume. Therefore, this study aimed to explore the allelopathic effects of A. pintoi under various screening conditions and to analyze its potential allelochemicals using gas chromatography–mass spectrometry (GC-MS). In laboratory bioassays, aqueous extracts of A. pintoi powder exerted the average inhibition of the growth of Echinochloa crus-galli (55.1%), Oryza sativa (77.1%), and Vigna radiata (60.1%), respectively, of which the root lengths of the tested plants were the most suppressed. In greenhouse experiments, E. crus-galli was inhibited by 63.4% at 200 g/m2 of A. pintoi dried powder application. In field trials, A. pintoi also significantly reduced the growth of E. crus-galli and natural weeds. By incorporating a dose of 200 g/m2, the average inhibition of E. crus-galli was 43.9%, the dry weight of natural paddy weeds was 43.1%, and rice yield was simultaneously increased by 35%. The growth inhibitions of weeds and tested plants were proportional to the doses of A. pintoi applied and varied with the tested plant species. Among three different solvent extracts (methanol, hexane, and ethyl acetate), the hexane extract exerted the highest suppression against the growth of E. crus-galli and L. sativa by IC50 against root and shoot growth = 4.08 and 8.4 mg/mL and 1.7 and 1.54 mg/mL, respectively, followed by ethyl acetate extract, while the least effective was methanol extract. From those extracts, a total of 35 substances were detected by GC-MS analyses, including 14 newly identified constituents, such as phenolic acids, stearic acid, palmitic acid, fatty acids, pyranones, and benzofurans, which may be responsible for the herbicidal effects of A. pintoi. This study suggests that A. pintoi may be used as a source of bioherbicide to minimize the dependency on harmful synthetic herbicides and enhance rice yield.