Specialized Metabolites from the Allelopathic Plant Retama raetam as Potential Biopesticides

Plant secondary metabolites-mediated plant defense against bacteria and fungi pathogens

Plant diseases caused by pathogenic bacteria and fungi are major threats to both wild plants and crops. To counteract these threats, plants have evolved various defense mechanisms, including the production of plant secondary metabolites (PSMs). These compounds, such as terpenoids, phenolics, alkaloids, and glucosinolates, offer a versatile, efficient, and cost-effective means of pathogen resistance. The traditional pathogen management methods relying on synthetic microbicides are often environment unfriendly. In contrast, PSMs provide promising alternative way due to their high efficiency and environmental benefits. This article reviews the categories, biosynthetic pathways, mechanisms of actions, and the commercialization of the PSMs to enhance our understanding of their pathogen resistance capabilities. The goal is to develop sustainable disease management strategies using PSM-based bactericides and fungicides.

Upcycling olive pomace into pectic elicitors for plant immunity and disease protection

Olive oil production generates substantial quantities of pomace, which are often disposed of in soil, leading to adverse effects on agriculture and the environment. Furthermore, climate change exacerbates plant diseases and promotes the use of toxic phytochemicals in agriculture. However, olive mill wastes can have high potential as reusable and valuable bioresources. Using diluted ethanol, an environmentally friendly solvent, we extracted a fraction containing short and long oligogalacturonides, short arabino-oligosaccharides and polysaccharides. The obtained extract elicited key features of plant innate immunity in Arabidopsis seedlings, including the phosphorylation of mitogen-activated protein kinases MPK3 and MPK6 and the upregulation of defence genes such as CYP81F2, WRKY33, WRKY53, and FRK1. Notably, pretreatment of adult Arabidopsis and tomato plants with the olive pomace extract primed defence responses and enhanced their resistance to the phytopathogens Botrytis cinerea and Pseudomonas syringae. Our results highlight the opportunity to upcycle the two-phase olive pomace collected at the late stage of olive oil campaign, in low-cost and sustainable glycan elicitors, contributing to reducing the use of chemically synthesized pesticides.

Chemical Composition and Phytotoxic and Antibiofilm Activity of the Essential Oils of Two Moroccan Retama Species

This study reports chemical composition, phytotoxic and antibiofilm activities of essential oils (EOs) of R. dasycarpa and R. sphaerocarpa from Morocco. EOs were analyzed by GC/MS and their phytotoxicities were evaluated against germination and seedling growth of Lolium multiflorum, Sinapis alba and Raphanus sativus. The antimicrobial and anti-biofilm activities were studied against Gram-negative (Pseudomonas aeruginosa, Escherichia coli and Acinetobacter baumannii) and Gram-positive bacteria (Staphylococcus aureus and Listeria monocytogenes). Both EOs were abundant in oxygenated monoterpenes (40.01% and 23.57 %, respectively). Carvacrol is the predominant component in R. dasycarpa EO (17.80 %), and it also represents an appreciable amount in R. sphaerocarpa (8.96 %). R. sphaerocarpa showed total inhibition at high doses against all seeds. S. alba seeds were the most sensitive to all EOs. Minimum inhibitory concentration (MIC) values indicated significant inhibition for R. sphaerocarpa, between 24 and 30 μg/mL, with a remarkable antibacterial potential and biofilm formation inhibition. R. sphaerocarpa EO showed significant biofilm inhibition with variable efficacy depending on the strain and concentration, except for S. aureus. R. dasycarpa exhibited activity against all bacterial strains and effect on metabolism with activity also on mature biofilms. Results suggest that Retama EOs could have potential applications in the fields of food and health.

Mediterranean Plants as Potential Source of Biopesticides: An Overview of Current Research and Future Trends

The development and implementation of safe natural alternatives to synthetic pesticides are urgent needs that will provide ecological solutions for the control of plant diseases, bacteria, viruses, nematodes, pests, and weeds to ensure the economic stability of farmers and food security, as well as protection of the environment and human health. Unambiguously, production of botanical pesticides will allow for the sustainable and efficient use of natural resources and finally decrease the use of chemical inputs and burden. This is further underlined by the strict regulations on pesticide residues in agricultural products and is in harmony with the Farm to Fork strategy, which aims to reduce pesticide use by 50% by 2030. Thus, the present work aims to compile the scientific knowledge of the last 5 years (2017-February 2023) regarding the Mediterranean plants that present biopesticidal effects. The literature review revealed 40 families of Mediterranean plants with at least one species that have been investigated as potential biopesticides. However, only six families had the highest number of species, and they were reviewed comprehensively in this study. Following a systematic approach, the extraction methods, chemical composition, biopesticidal activity, and commonly used assays for evaluating the antimicrobial, pesticidal, repellant, and herbicidal activity of plant extracts, as well as the toxicological and safety aspects of biopesticide formulation, are discussed in detail. Finally, the aspects that have not yet been investigated or are under-investigated and future perspectives are highlighted.

Iridoid Glycosides Isolated from Bellardia trixago Identified as Inhibitors of Orobanche cumana Radicle Growth

Orobanche cumana is an obligate holoparasitic plant with noxious effects in sunflower crops. Bellardia trixago is a facultative hemiparasitic plant that infects ruderal plants without noxious significance in agriculture and is known to produce a wide spectrum of bioactive metabolites. The objective of this study was to evaluate the allelopathic effects of B. trixago on the growth of O. cumana seedlings. Three different extracts using solvents of increasing polarity (n-hexane, dichloromethane and ethyl acetate) were prepared from the flowers, aerial green organs and roots of two populations, a white-flowered and a yellow-flowered population of B. trixago, both collected in southern Spain. Each extract was studied using allelopathic screenings on O. cumana which resulted in the identification of allelopathic activity of the ethyl acetate extracts against Orobanche radicles. Five iridoid glycosides were isolated together with benzoic acid from the ethyl acetate extract of aerial green organs by bio-guided purification. These compounds were identified as bartsioside, melampyroside, mussaenoside, gardoside methyl ester and aucubin. Among them, melampyroside was found to be the most abundant constituent in the extract (44.3% w/w), as well as the most phytotoxic iridoid on O. cumana radicle, showing a 72.6% inhibition of radicle growth. This activity of melampyroside was significantly high when compared with the inhibitory activity of benzoic acid (25.9%), a phenolic acid with known allelopathic activity against weeds. The ecotoxicological profile of melampyroside was evaluated using organisms representing different trophic levels of the aquatic and terrestrial ecosystems, namely producers (green freshwater algae Raphidocelis subcapitata and macrophyte Lepidium sativum), consumers (water flea Daphnia magna and nematode Caenorhabditis elegans) and decomposers (bacterium Aliivibrio fischeri). The ecotoxicity of melampyroside differed significantly depending on the test organism showing the highest toxicity to daphnia, nematodes and bacteria, and a lower toxicity to algae and macrophytes. The findings of the present study may provide useful information for the generation of green alternatives to synthetic herbicides for the control of O. cumana.