Both saprophytic soil fungi and those living as endophytes have the potentiality to shape and modulate the stress tolerance in plants. These fungi can operate by eliciting or increasing defence responses in the plant or indirectly through complex mechanisms of competition for substrates. This aspect assumes an even greater relevance when these metabolites have a pharmacological potential.
The objective of the proposal is to develop a strategy for the sustainable cultivation of the medicinal plant Hypericum perforatum (L.) through the use of multifunctional soil bioinoculants and the application of water-soluble fungal elicitors to the aerial organs.
The treatments will be aimed to: i) promote the plant growth; ii) enhance the biosynthesis of bioactive secondary metabolites, including hypericin, hyperforin, essential oils, flavonoids and xanthones; iii) induce resistance to disease; iv) increase the antifungal activity of root and shoot extracts; v) reduce the use of chemical fertilisers and synthetic compounds both against plant and human pathogens.
Bioinocula will be chosen among fungal species already known for their growth-promoting activity (Minimedusa polyspora) and for living in association with H. perforatum as endophytic fungi (e.g. Chaetomium globosum).
H. perforatum aerial parts will be treated by nebulization with chitosan oligosaccharides (COS), already known as growth-promoting substances and for their elicitor power on xanthone biosynthesis in the roots.
Antifungal tests will be carried out against two of the main H. perforatum fungal pathogens (Colletotrichum gloeosporioides and Phomopsis sp.), in order to investigate disease resistance as induced by the selected saprotrophic fungi and the treatment with COS.
The antimicrobial activity of extracts obtained from H. perforatum plants treated with saprotrophic fungi and/or COS will be evaluated on human fungal pathogens, such as Candida species and dermatophytes.
1) Use of saprotrophic fungi as a strategy for the sustainable cultivation of the medicinal plant HP
The proposed strategy will be aimed to reduce the use of chemical compounds such as fertilizers and pesticides, massively used in traditional agriculture. This strategy will be crucial to avoid the contamination of the final product. In this regard, it should be stressed that HP preparations are generally obtained from total extracts, that are not subjected to purification.
In accordance with Directive 2009/128/EC, this integrated strategy could be extended to other medicinal plants, as well as to food plants cultivated for human and animal use. In addition to the growth promotion, the proposed strategy is also designed to activate the plant defenses, including the neo-synthesis of phytoalexins. Considering that these defense compounds are also responsible for the most of biological activities of HP, the increase of metabolite concentration will improve the therapeutic potential of the drug.
2) Use of HP as a topic antifungal agent
HP has been intensively investigated for its anti-depressive activity, but dermatological applications also have a long tradition. Topical HP preparations such as oils or tinctures are used for the treatment of minor wounds and burns, sunburns, abrasions, and many others (Wölfle et al. 2014 Planta Med 80:109). We have previously investigated the antifungal activity of HP extracts against human fungal pathogens (Valletta et al 2016 Plant Cell Rep 35:1009; Simonetti et al. 2016 Nat Prod Res 30:544). The purposed strategy to fight fungal plant pathogens could also increase the antifungal activity against human fungal pathogens.
3) Multifunctional soil bioinoculants: challenges to improve HP cultivation
The untapped potential of fungi has been revealed by many researches regarding their application not only to improve environmental quality but also human health. We have previously investigated that fungi can play several ecological roles in ecosystems and in some fungal species more than one roles can be performed with a wide multifunctionality and plasticity (Ceci et al 2018 Ambio 47:30). Multifunctional soil bioinoculants represent an effective toolbox for a sustainable cultivation of the medicinal plants.
We believe that the proposed research provides new insights into environmental sustainability and human health, in order to reduce the use of chemical fertilizers and synthetic compounds both against plant and human pathogens.