Metabolite Screening From Pinus pinea Needles Reveals (+)-Isocupressic Acid as a Key Phytotoxin for Weed Management.

Introduction: Weeds are a major threat to crop productivity, competing for essential resources and often developing resistance to herbicides, which underscores the need for novel, sustainable control strategies. The valorization of agricultural and forestry underutilized byproducts, such as plant needles, presents a promising opportunity for developing eco-friendly bioherbicides based on allelopathy.

Objectives: This study investigates the phytotoxicity of Pinus pinea needle extracts and metabolites to evaluate their potential for controlling dicotyledonous weeds.

Material and methods: The chemical characterization of extracts and isolated compounds was performed via GC-MS, NMR, and optical methods while phytotoxicity bioassays were carried out using the herbicides Pacifica Plus (Bayer CropScience) and pendimethalin, the active ingredient in Stone Aqua (Tokyo Chemical Industry), as positive controls.

Results: The dichloromethane extract exhibited the highest phytotoxicity, significantly inhibiting Portulaca oleracea and Plantago lanceolata weeds. GC-MS analysis revealed an array of aromatic compounds of interest for phytochemical research, and through bio-guided purification, five lignans and the diterpenic acid (+)-isocupressic acid were isolated. (+)-Isocupressic acid showed the strongest phytotoxicity on P. oleracea, particularly on root growth (-83% ± 4% at 1000 μM), which could be correlated with structural moieties in its structure (fused-ring scaffold with an exocyclic double bond, an exocyclic chain containing a double bond or hydroxyl group, and a carboxylic acid group), a number of H-bond donors ≤ 2, and higher lipophilicity (Clog p = 5.11). Some lignans displayed mild inhibitory or stimulatory effects on P. lanceolata.

Conclusion: P. pinea needle extracts and metabolites have demonstrated potential as natural bioherbicides for weed management. Further research is prompted to explore large-scale applicability, environmental safety through ecotoxicological studies, and optimized formulations to enhance their practical use in sustainable agriculture.