Herbicidal Phytotoxic activity and chemical characterization of Baccharis halimifolia L. (Asteraceae) aqueous extracts

Giacomo Trespidi^1,2*Valeria Xotta^3,4Stefania Sut^3,5Stefan Otto^1,2Nebojša Nikolić^3,4Elisa Strati^1,2Sara Vitalini^6,7Stefano Dall'Acqua^3,5Marcello Iriti^6,7Roberta Masin^3,4Donato Loddo^1,2

• ¹National Research Council (CNR), Roma, Italy
• ²Institute for Sustainable Plant Protection, National Research Council (CNR), Turin, Piedmont, Italy
• ³University of Padua, Padua, Veneto, Italy
• ⁴Department of Agronomy, Food, Natural Resources, Animals and the Environment, School of Agricultural Sciences and Veterinary Medicine, University of Padua, Legnaro, Veneto, Italy
• ⁵Department of Pharmaceutical Sciences, School of Medicine and Surgery, University of Padua, Padua, Veneto, Italy
• ⁶University of Milan, Milan, Lombardy, Italy
• ⁷Department of Biomedical, Surgical and Dental Sciences, Faculty of Medicine and Surgery, University of Milan, Milan, Lombardy, Italy

The development search for environmentally friendly new tools appear to be crucial to ensure sustainable weed management and the study of allelochemicals in plants plays a strategic role in the eco-friendly agrochemical development. This study aims, for the first time, to evaluate the presence of allelopathic substances and the herbicidal activity of aqueous extracts from the leaf (BL) and root (BR) wastes to identify and quantify allelopathic substances in aqueous extracts from leaves (BL) and roots (BR) of the invasive species Baccharis halimifolia L. (Asteraceae) and to assess their phytotoxic activity at different dilutions in both germination tests and greenhouse pot trials for the weed species Abutilon theophrasti Medik., Solanum nigrum L., Lolium rigidum Gaudin and Setaria pumila Roem. & Schult. HPLC-DAD-(ESI)-MS analysis revealed the presence of several saponins and phenolics (e.g. Apigenin and Protocatechuic acid), possibly implicated in the observed phytotoxic action. The most relevant effects were observed in the germination test, where BR was more effective than BL and at 20% v/v concentration dilution caused a 50-75% reduction in root length of all weed species. Maximum reduction (>85%) in root length occurred at 100% v/v concentration dilution of both extracts for all species. Pre-and post-emergence greenhouse trials showed unstable and variable herbicidal activity among the tested species and extract doses. Effects were observed in particular mainly on the grasses S. pumila and L. rigidum, where BR application in post-emergence reduced plant biomass by 42% and 34%. This study confirmed the presence of phytotoxic compounds in aqueous extracts of B. halimifolia suggesting suggests that B. halimifolia it could be a potential source of natural herbicides; . Hhowever, it also highlighted showed the difficulties in reproducing, under the field-like conditions of pot trials, the phytotoxic effects ha formattato: Tipo di carattere: Corsivo observed in germination tests due to radical differences in applied doses and exposure conditions. This highlights the importance of studies that consider field application and the need of green extraction methodologies that improve active substances concentration in extract.