SUMMARY Research background: Many plant extracts and essential oils show antibacterial and antifungal activities, with potential to replace the use of synthetic fungicides. We used invasive alien plants goldenrod (Solidago spp.) and Japanese knotweed (Fallopia japonica) as source materials to determine their antifungal activities against seed-associated fungi from wheat grain (Alternaria alternata, Alternaria infectoria, Aspergillus flavus, Epicoccum nigrum and Fusarium poae). Experimental approach: Aqueous and organic extracts (ethanol, methanol, acetone) were prepared from leaves and flowers of S. canadensis, S. gigantea and S. virgaurea, and leaves and rhizomes of F. japonica. Additionally, essential oils were distilled from Solidago flowers and leaves. The extracts and essential oils were tested as inhibitors of fungal growth in vitro. Solidago essential oils were tested also as antifungal agents for protection of wheat grain determining its fungal infection and germination rate. Results and conclusions: The extracts showed a wide spectrum of low to moderate antifungal activities, with those of Solidago spp. generally more effective than those of F. japonica, with organic extracts more effective than aqueous extracts. The essential oils from leaves and flowers had similar antifungal activity and whole shoots can be collected for their production. This study presents the systematic study of the composition of essential oils from flowers and leaves of three widely distributed Solidago spp. in Slovenia, with the major constituents of terpenes and terpenoids α-pinene, germacrene D and bornyl acetate. Novelty and scientific contribution: The study presents the first use of Solidago spp. and Fallopia japonica extracts and essential oils against fungal strains isolated from wheat grain.

Fungal infections of cultivated food crops result in extensive losses of crops at the global level, while resistance to antifungal agents continues to grow. Supercritical fluid extraction using CO₂ (SFE-CO₂) has gained attention as an environmentally well-accepted extraction method, as CO₂ is a non-toxic, inert and available solvent, and the extracts obtained are, chemically, of greater or different complexities compared to those of conventional extracts. The SFE-CO₂ extracts of Achillea millefolium, Calendula officinalis, Chamomilla recutita, Helichrysum arenarium, Humulus lupulus, Taraxacum officinale, Juniperus communis, Hypericum perforatum, Nepeta cataria, Crataegus sp. and Sambucus nigra were studied in terms of their compositions and antifungal activities against the wheat- and buckwheat-borne fungi Alternaria alternata, Epicoccum nigrum, Botrytis cinerea, Fusarium oxysporum and Fusarium poae. The C. recutita and H. arenarium extracts were the most efficacious, and these inhibited the growth of most of the fungi by 80% to 100%. Among the fungal species, B. cinerea was the most susceptible to the treatments with the SFE-CO₂ extracts, while Fusarium spp. were the least. This study shows that some of these SFE-CO₂ extracts have promising potential for use as antifungal agents for selected crop-borne fungi.