Evaluation of the Phytotoxicity of Urochloa humidicola Roots by Bioassays and Microscopic Analysis. Characterization of New Compounds

Abstract

Herbicides are a key element in agriculture but they do cause environmental problems and natural alternatives are being sought. In this context, invasive plants could provide an as yet unexplored source for the development of future herbicides. Urochloa humidicola has great invasive potential in Brazilian environments as it hampers the establishment of other plants. The phytotoxicity of U. humidicola root extracts has been evaluated, and the major components have been identified. The phytotoxicity of the extract was assessed in the wheat coleoptile assay on seeds of troublesome weeds and on Anadenanthera colubrina, a tree species used in ecological restoration programs. The ethyl acetate extract showed the highest activity, and the most affected weeds were E. crus-galli, M. maximus, and A. viridis with the latter weed more affected by the extract than by the herbicide Logran. Microscopic ultrastructural analysis of A. colubrina roots indicated possible signals of cell death. Seven compounds were identified in the ethyl acetate extract of which one diterpene and four saponins are new. Six of these compounds were tested in the wheat coleoptile bioassay. The most active were diterpene 1 and saponins 2, 3, and 6. The phytotoxic activity of U. humidicola explains the issues observed in ecological restoration with A. colubrina in the presence of Urochloa species, and its effect on weeds reinforces its potential use in agriculture.

Flow Cytometry-Based Determination of Ploidy from Dried Leaf Specimens in Genomically Complex Collections of the Tropical Forage Grass Urochloa s. l.

“…Seasonal and regional differences in accumulation of secondary products may cause differences in staining for flow cytometry. Secondary metabolites and their phytotoxicity on forage legumes have been recognized in Urochloa tropical forage grasses [ 21 , 22 , 23 , 24 ], which has been suggested to make it difficult to analyze these plants by flow cytometry [ 25 ].…”

Root exudate fingerprint of Brachiaria humidicola reveals vanillin as a novel and effective nitrification inhibitor

“…These comprise brachialactol, different flavones (especially quercetin glycosides) and saponins, but especially different phenolic acids, i.e., p -coumaric acid, p -hydroxy-benzoic acid and vanillic acid ( Supplementary Table S12 ; Supplementary Material ). These allelopathica have been proposed to be responsible for the suppression of companion plants (e.g., grass-legume mixtures) and responsible for the dominance of B. humidicola in many ecosystems ( Souza Filho et al, 2005 ; Oliveira et al, 2017 ; Feitoza et al, 2018 ; Feitoza et al, 2020 ). However, with regard to nitrification inhibition, none of the discussed phenolic acids ( p -coumaric acid, ferulic acid, p -hydroxy-benzoic acid, vanillic acid) showed inhibitory activity against N. europaea , which was tested in vitro with concentrations up to 100 mg·L −1 (data not shown).…”

Model-Based Analysis of Lactuca sativa Root Growth under the Action of Herbicides in Milli-Channel Arrays with In Situ Imaging

“…In the past few years, metabolic, cytotoxic, and phytotoxic − studies have been carried out to assess the ecosystem impact of anthropogenic activities. In the field of ecotoxicology, the use of plant phytotoxicity tests has being continuously growing from the 1970s, − as they have been shown to be valuable indicators for environmental monitoring and toxicity assessment of pure soluble compounds, complex mixtures, and waters (surface, ground, domestic, industrial, and soil leachates). In particular, Lactuca sativa is a model organism that has been recommended for phytotoxicity testing in the guidelines issued by competent organizations. − In fact, the germination of these seeds and the subsequent root growth are very susceptible to the presence of herbicides such as 2,4-D (2,4-dichlorophenoxy acetic acid), atrazine (2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine), glyphosate ( N -phosphonomethyl glycine), and paraquat (1,1-dimethyl-4,4-bipyridinium dichloride).…”