Rue and Ash Leaf Extracts Show Potent Antifungal Power Against Cereal Fusarium Pathogens

A team of researchers in Algeria and Tunisia has reported that leaf extracts from two familiar Mediterranean medicinal plants, Ruta chalepensis, commonly known as fringed rue, and Fraxinus angustifolia, the narrow-leafed ash, can strongly inhibit the growth of Fusarium fungi that attack cereal crops. The study, published in the journal Plant Biosystems, is notable not only for the potency of the extracts but also because it represents the first documented evaluation of maceration, ultrasound-assisted and microwave-assisted extracts of these two species against Fusarium redolens, an emerging cereal pathogen that has received far less attention than better-known relatives such as Fusarium culmorum and Fusarium graminearum. The findings arrive at a moment when agriculture urgently needs alternatives to synthetic fungicides, many of which are losing effectiveness as resistance spreads through fungal populations.

Fusarium species are among the most economically damaging pathogens of wheat, barley, maize and other cereals worldwide. They cause seedling blight, crown and root rot, and the devastating head blight of wheat and barley, and they contaminate grain with mycotoxins such as deoxynivalenol and other trichothecenes that threaten food and feed safety. Managing these fungi has relied heavily on triazole-based fungicides and crop rotation, yet chemical control is imperfect, and meta-analyses of triazole efficacy against Fusarium head blight and deoxynivalenol accumulation show only partial protection. Resistance to fungicides within Fusarium populations is an increasing concern, and regulatory pressure on agrochemicals continues to grow. Against this backdrop, plant-derived phenolic compounds have attracted attention as possible biopesticides, since plants themselves deploy these molecules as chemical defenses against fungal invaders.

The research team, led by Farah Hamici of the University of Bouira in Algeria, together with colleagues from Bouira and Jendouba University in Tunisia, set out to answer two linked questions: how the choice of extraction technology and solvent shapes the phytochemical profile of the two plants, and whether the resulting extracts differ in their ability to suppress Fusarium growth. The researchers compared three environmentally friendly extraction techniques: conventional maceration, ultrasound-assisted extraction, which uses acoustic cavitation to rupture plant cell walls, and microwave-assisted extraction, which heats intracellular water rapidly to burst cells from within. Each technique was performed with two solvents, distilled water and a 70 percent ethanol solution, giving a matrix of six extraction conditions per plant.

The quantitative results demonstrated that both the method and the solvent significantly influenced phytochemical recovery. Microwave-assisted extraction generally delivered the highest total phenolic contents, consistent with the idea that rapid internal heating liberates phenolics more completely than slower techniques. Ultrasound-assisted extraction with the hydroethanolic solvent, by contrast, proved especially effective for flavonoids, a subclass of polyphenols that includes many well-known antifungal and antioxidant agents. The authors note that this kind of method-dependent variation matters practically, because a bioactivity observed in one extract may vanish in another prepared from the same plant with a slightly different protocol. Standardizing extraction is therefore a prerequisite for any serious attempt to turn these plants into reproducible crop-protection products.

Antioxidant performance was assessed with two standard radical-scavenging assays, DPPH and ABTS, which measure how effectively an extract neutralizes synthetic free radicals. Ruta chalepensis emerged as the stronger and more consistent antioxidant of the two species. Its DPPH half-maximal inhibitory concentrations, or IC50 values, ranged from 3.5 to 4.7 micrograms per milliliter, remarkably low figures that indicate very potent radical scavenging, while ABTS values ranged from 4.0 to 13.8 micrograms per milliliter. Fraxinus angustifolia, whose manna and bark have long been valued in Mediterranean traditional medicine and whose phenolic composition has been characterized in earlier work, showed antioxidant activity as well, though less consistently across the extraction conditions.

The antifungal assays formed the heart of the study. The team tested the extracts in vitro against two cereal-associated pathogens, Fusarium redolens and Fusarium culmorum, using methods adapted from standardized microtiter plate monitoring protocols for Fusarium growth. The results pointed clearly in one direction: Fusarium redolens was the more susceptible of the two species, and the hydroethanolic extracts of Ruta chalepensis were the most inhibitory preparations overall. Minimum inhibitory concentrations, or MIC values, for the most active rue extracts fell below 50 micrograms per milliliter against Fusarium redolens, an impressively low threshold for a crude plant extract, and ranged from 79.34 to 82.38 micrograms per milliliter against the more tolerant Fusarium culmorum. Extracts of Fraxinus angustifolia also inhibited both fungi, but generally required higher concentrations.

To understand which molecules might be responsible, the researchers subjected the most active extracts to HPLC-DAD analysis, a chromatographic technique that separates compounds and detects them by their absorption of ultraviolet and visible light. Among the compounds showing the largest relative peak areas in the most active preparations were quercetin and a dihydroxyflavone. Quercetin in particular has an extensive literature behind it: studies of its antimicrobial mechanisms describe multiple modes of action, including disruption of fungal membrane integrity, inhibition of energy metabolism and interference with cell wall biosynthesis. The presence of these flavonoids at high relative abundance in the extracts that performed best against the fungi suggests, though it does not yet prove, that they contribute substantially to the observed antifungal effect.

An important caveat, and one that the broader literature on natural products emphasizes, is that crude plant extracts are not single drugs but complex mixtures whose components may interact synergistically or antagonistically. Researchers studying natural product extracts have repeatedly shown that whole extracts can outperform any isolated constituent, because multiple compounds attack multiple fungal targets simultaneously, making resistance harder to evolve. The Algerian team’s finding that hydroethanolic rue extracts, rich in several phenolics at once, were the most fungistatic preparations is consistent with such a multi-component mode of action. It also echoes earlier reports of antifungal activity in Ruta species, including work on rue essential oils from the Moroccan High Atlas and on enriched extracts of Ruta graveolens against other Fusarium species.

The choice of Fusarium redolens as a test organism gives the study particular significance. This soil-borne species has been flagged in recent reviews as an emerging plant pathogen, notably in Iran, where it has been implicated in cereal root rots, yet it remains understudied relative to its headline-grabbing relatives. Because no previous study had evaluated macerated, ultrasound-assisted or microwave-assisted extracts of either rue or narrow-leafed ash against this fungus, the low MIC values reported here establish a genuine first. They also suggest that phenolic-rich extracts could be integrated into management strategies for crown and root rot diseases, which are receiving renewed attention across North African wheat-growing regions as climate variability alters disease pressure.

Several steps remain before any of this translates into a field-ready biopesticide. In vitro inhibition of mycelial growth does not guarantee efficacy on seeds or in soil, where extract stability, rainfastness, phytotoxicity to the crop and effects on beneficial soil microbes all come into play. Whether the extracts also suppress mycotoxin production, not just fungal growth, is a separate and critical question, since phenolic compounds have been shown in some systems to reduce trichothecene biosynthesis and in others to have no such effect. Formulation, scale-up of extraction and cost analysis will determine whether microwave- or ultrasound-assisted hydroethanolic extraction of rue leaves is economically viable at agricultural scale. Nevertheless, the study offers a compelling proof of concept: two plants with deep roots in Mediterranean folk medicine, extracted with green technologies and simple solvents, produce preparations that stop a cereal pathogen at concentrations measured in tens of micrograms per milliliter. As fungicide resistance spreads and consumers demand lower chemical residues in food, such plant-based defenses are moving from ethnobotanical curiosity toward practical crop protection, and this first look at rue and ash against Fusarium redolens suggests they deserve a place in that conversation.

Subject of Research: Antifungal activity of phytochemical extracts from Ruta chalepensis and Fraxinus angustifolia against cereal Fusarium pathogens

Article Title: Phytochemical characterization and antifungal activity of Fraxinus angustifolia and Ruta chalepensis against cereal Fusarium species: first evaluation against Fusarium redolens

Article References: Phytochemical characterization and antifungal activity of Fraxinus angustifolia and Ruta chalepensis against cereal Fusarium species: first evaluation against Fusarium redolens. (n.d.). https://doi.org/10.1007/s44473-026-00246-x

Image Credits: AI Generated

DOI: 10.1007/s44473-026-00246-x

Keywords: Ruta chalepensis, Fraxinus angustifolia, Fusarium redolens, Fusarium culmorum, antifungal activity, plant extracts, phenolic compounds, quercetin, microwave-assisted extraction, ultrasound-assisted extraction, biopesticides, cereal pathogens