Novel and holistic approaches are required to realize allelopathic potential for weed management

Phytochemical Analysis and Allelopathic Potential of an Aggressive Encroacher Shrub, Euryops floribundus (Asteraceae)

Euryops floribundus is an encroaching shrub species that poses a threat to grassland diversity and productivity in the Eastern Cape region of South Africa. This shrub inhibits understory herbaceous plant recruitment and establishment, thereby exposing soils to erosion, owing potentially to toxins it secretes. However, the allelochemicals of E. floribundus and their potential effects on the germination and establishment of plants remains poorly understood. We investigated the phytochemical classes of leaves and twigs of E. floribundus and evaluated the effects of extracts from these plant parts on seed germination and seedling growth of Lactuca sativa through a laboratory experiment. In the laboratory, we analysed phytochemicals in leaf and twig extracts and tested their allelopathic effects on Lactuca sativa seed germination and growth using the Petri dish method. In this proof-of-concept study, we identified 12 phytochemical classes of E. floribundus. Quantitative analysis showed that the leaves had significantly higher levels of flavonoids, phenolics, and tannins than twigs. As a result, leaf extracts caused 100% inhibition of seed germination, while twig extracts inhibited seed germination by 90% at 50 g L-1. Both leaf and twig extracts also significantly reduced radicle and plumule growth, with a stronger effect observed from the leaves than twigs. This study provides new insights into the phytochemical composition and strong allelopathic potential of E. floribundus, contributing to a better understanding of the mechanisms driving its encroachment in semi-arid grasslands.

Optimized extraction methodology for phenolic compounds in soil and plant tissues: Their implications in plant growth and gall formation

Phenolic compounds, abundant secondary metabolites in plants, profoundly influence soil ecosystems, plant growth, and interactions with herbivores. Phenolic in soil microorganisms have the potential to impact a wide range of activities in plant-soil interactions. However, the existing methods for measuring microbial activity are typically time-consuming, intricate, and expensive. In this study, we propose modifications to the method used for the extraction and quantification of various types of phenolics in soil and plant tissues. There have been substantial advancements in research aimed at extracting, identifying, and quantifying phenolic compounds in the plant and soil samples. This study discusses the use of different methodologies in the analysis of phenolic compounds. In addition, we investigated the effect of phenolics on plant growth and cues in gall-forming under environmental disturbances.•This method is the optimum way to extract phenolic from soil and microbial activity in bulk and rhizosphere soil.•It can be used on any soil type and plant tissue, metabolites extracted from living organisms.

Optimizing Allelopathy Screening Bioassays by Using Nano Silver

Nano solutions are widely used in medicine and also have the potential to be used when performing allelopathy screening studies. The present experiment aimed to test the effectiveness of colloidal nano silver Silver-Amber© with nanoparticles of 20 nm (>20 mg/L at a purity level of 99.99%) as a carrier of allelochemicals in laboratory conditions. The influence of eleven concentrations of Silver-Amber© (0.10, 0.20, 0.39, 0.78, 1.56, 3.13, 6.25, 12.5, 25.0, 50.0 and 100.0% v/v) on the germination and initial development of test plant Lactuca sativa L. in 0.75% agar medium was studied. Data revealed that when increasing the quantitative ratio of Silver-Amber©, an inhibitory effect on seed germination (from 37.8 to 94.3%) and on the plant growth (from 54.0 to 98.9%) appeared. Lower concentrations (0.63 to 0.04 ppm) had an indifferent to statistically unproven stimulatory effect on the germination and initial development of L. sativa (GI ranged from 88.7-94.6%). Therefore, nano silver can be used as carrier of allelochemicals in allelopathic studies in laboratory conditions.

Effect of phenolics on soil microbe distribution, plant growth, and gall formation

Phenolic compounds, abundant secondary metabolites in plants, profoundly influence soil ecosystems, plant growth, and interactions with herbivores. In this study, we explore the intricate relationships between phenolics, soil microbes, and gall formation in Ageratina adenophora (A. adenophora), an invasive plant species in China known for its allelopathic traits. Using metabolomic and microbial profiling, significant differences in soil microbial composition and metabolite profiles were observed between bulk and rhizosphere soil samples. Phenolics influenced bacterial communities, with distinct microbial populations enriched in each soil type. Additionally, phenolics impacted soil metabolic processes, with variations observed in Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis between different soil treatments. Analysis of phenolic content in plant and soil samples revealed considerable variations, with higher concentrations observed in certain plant tissues and soil types. Bioactive phenols extracted from plant and soil samples were identified using gas chromatography/mass spectrometry (GC-MS), providing insights into the diverse chemical composition of these compounds. Furthermore, the effects of phenolics on plant growth and gall formation were investigated. Phenols exhibited both stimulatory and inhibitory effects on plant growth, with optimal concentrations promoting emergence but higher concentrations hindering growth. Gall formation was influenced by phenolic concentrations, leading to structural alterations in stem tissue and gall morphology. Histochemical analysis revealed starch and lipid accumulation in gall tissues, indicating metabolic changes induced by phenolics. The presence of phenolics disrupted tissue structures and influenced vascular bundle orientation in gall tissues. Overall, our study highlights the multifaceted roles of phenolic compounds in soil ecosystems, plant development, and gall formation, facilitating the utilization of secondary metabolites in agriculture.

The Aqueous Extract of Brassica oleracea L. Exerts Phytotoxicity by Modulating H2O2 and O2- Levels, Antioxidant Enzyme Activity and Phytohormone Levels

Allelopathic interactions between plants serve as powerful tools for weed control. Despite the increasing understanding of the allelopathic mechanisms between different plant species, the inhibitory effects of B. oleracea on weed growth remain poorly understood. In this study, we conducted experiments to demonstrate that B. oleracea extract can suppress the germination of Panicum miliaceum L.varruderale Kit. seeds as well as of the roots, shoots and hypocotyl elongation of P. miliaceum seedlings. Furthermore, we observed that B. oleracea extract reduced the levels of hydrogen peroxide and superoxide anion in the roots while increasing the activities of catalase and ascorbate peroxidase. In the shoots, B. oleracea extract enhanced the activities of superoxide dismutase and peroxidase. Moreover, the use of the extract led to an increase in the content of phytohormones (indole-3-acetic acid, indole-3-acetaldehyde, methyl indole-3-acetate, N6-isoPentenyladenosine, dihydrozeatin-7-glucoside, abscisic acid and abscisic acid glucose ester) in P. miliaceum seedlings. Interestingly, the aqueous extract contained auxins and their analogs, which inhibited the germination and growth of P. miliaceum. This may contribute to the mechanism of the B. oleracea-extract-induced suppression of P. miliaceum growth.