Phytotoxic Metabolites from Hyptis Species: Chemical Profiling and Bioherbicide Activity Against Amaranthus

Abstract

The phytotoxic effects of extracts from Hyptis crenata (Hcre), Hyptis suaveolens (Hsua), Hyptis saxatilis (Hsax), Hyptis campestris (Hcam), and Hyptis brevipes (Hbre) were evaluated against three Amaranthus weed species under controlled germination chamber conditions. Extracts Hcre, Hsua and Hsax inhibited seed germination by 85–93% relative to the control and markedly suppressed radicle and hypocotyl growth in Amaranthus viridis and Amaranthus hybridus in Petri dish assays. At 200 ppm, Hcre and Hsax reduced radicle and hypocotyl lengths by up to 90% in both species, comparable to the effects of commercial herbicides Sencor and Sulfentrazone. Multivariate analyses, including PCA, PLS-DA, and molecular networking based on LC-MS/MS data, enabled the annotation of compounds associated with phytotoxicity. A total of 56 metabolites were identified, including terpenoids, flavonoids, α-pyrones, carbohydrate derivatives, and polyketides, using both an in-house database and the GNPS platform. Terpenoids were the predominant class, with abietane-type diterpenes as the most abundant subgroup, exhibiting strong correlations with the observed biological activity.