The (in)visible side of biostimulation: application of 1H-NMR to reveal the biostimulating effect of Minimedusa polyspora and Chaetomium globosum culture filtrates on Cichorium intybus plants

Finding environmentally friendly and climate-resilient agronomic solutions to increase food production while addressing modern agriculture’s issues is the biggest challenge our society is currently facing. In this context, biostimulants represent a sustainable solution to increase crop resilience and productivity in adverse environmental conditions, while minimizing agrochemicals applications and tackling climate change effects [1,2]. Cichorium intybus L. (chicory), Asteraceae family, is an alimurgic plant whose popularity is steadily increasing due its rich and complex phytochemical profile, including a great number of bioactive substances, and a high nutritional value which make it a plant of agricultural and medicinal importance [3]. Therefore, this study aimed at investigating the biostimulant effect of fungal culture filtrates of Chaetomium globosum and Minimedusa polyspora on growth performance and metabolomic traits of C. intybus plants. In a pot experiment set up in walk-in chambers, chicory plants, one month after the transfer of the seedlings in pots, were stimulated by soil drenching with 8 ml/ pot (30 ml/kg of soil) of the culture filtrates obtained by a 14-days incubation of the fungal strains in Malt Extract Broth (MEB), or the same amount of uninoculated MEB in the control group. Fourteen days after the stimulation, plant biomasses were recovered to estimate several growth parameters and analyze the metabolomic variations occurred in roots and leaves through 1H-NMR 600 MHz. We observed for the first time that M. polyspora culture filtrate promotes an increase of biomass, both in shoots and roots, and of the leaf area, while no increase was observed in plants treated with C. globosum culture filtrate. Based on 1H-NMR metabolomics data, differential metabolites and their related metabolic pathways were highlighted. A common response in C. intybus roots involving the synthesis of 3-OH-butyrate through the decrease of the synthesis of fatty acids and sterols, as a mechanism balancing the NADPH/NADP+ ratio, was observed in both the treatments with C. globosum and M. polyspora culture filtrates. The phenylpropanoid pathway was differently triggered by the fungal culture filtrates. C. globosum culture filtrate increased phenylalanine and chicoric acid in the roots. Chicoric acid, whose biosynthetic pathway in chicory plant is putative and still not well known, is a very promising natural compound playing an important role in plant defense. Instead, M. polyspora culture filtrate interestingly stimulated an increase of 4-OH benzoate, being benzoic acids precursors for a wide variety of essential compounds playing crucial roles in plant fitness and defense response activation. Therefore, both C. globosum and M. polyspora culture filtrates determined interesting modification in C. intybus metabolome. 1. Sangiorgio et al., 2020. Application of Microbial Biostimulants to Mitigate Stress in Horticultural Crops. doi:10.3390/agronomy10060794. 2. Castiglione et al., 2021. Microbial Biostimulants as Response to Modern Agriculture Needs: Composition, Role and Application of These Innovative Products. doi:10.3390/plants10081533. 3. Janda et al., 2021. The Common Cichory (Cichorium intybus L.) as a Source of Extracts with Health-Promoting Properties—A Review doi:10.3390/molecules26061814.