Cyttaria hariotii E.Fisch. as a promising source of pullulan and Mn(II)-pullulan complexes for Mn-deficiency remediation in winter cereals

Pullulan, a water-soluble polysaccharide consisting of maltotriose units used in the preparation of edible films and drug delivery, is generally produced from starch by Aureobasidium pullulans (de Bary & Löwenthal) G.Arnaud fungus. In this article, the characterisation of an alternative pullulan source - the stromata of Cyttaria hariotii E.Fisch. fungus - by elemental analysis, infrared spectroscopy and thermal analysis techniques is reported. With a view to a possible valorisation of this pullulan and its derivatives as bioactive formulations in agriculture, low-molecular-weight pullulan (<7 kDa) complexes with Mn(II), suitable for the remediation of Mn-deficiencies in winter cereal by foliar application, were synthesised and characterised by mass spectrometry

Physicochemical characterization and antimicrobial activity against Erwinia amylovora, Erwinia vitivora, and Diplodia seriata of a light purple Hibiscus syriacus L. Cultivar

Phytochemicals are essential raw materials for the production of formulations that can be helpful in crop protection. In particular, Hibiscus spp., which are often used in traditional medicine, are rich in potential bioactive molecules. This study presents an analysis of the thermal, vibrational, and phytochemical characteristics of a light purple variety of Hibiscus syriacus, using thermal gravimetric and differential scanning calorimetry, Fourier-transform infrared spectroscopy, and gas chromatography-mass spectroscopy techniques. Further, with a view to its valorization, the antimicrobial activity of its extracts has been investigated in vitro against Erwinia amylovora (the phytopathogen responsible for fire blight in apples, pears, and some other members of the family Rosaceae), Erwinia vitivora (the causal agent of the “maladie d’Oléron” in grapevines), and Diplodia seriata (responsible for “Bot canker”). Higher heating values and thermal features showed similarities with kenaf biomass. The main compounds identified in the hydro-methanolic extracts were: in flowers, 1-heptacosanol, heptacosane, 1-tetracosanol, hexadecenoic acid, 9,12,15-octadecatrienoic acid, and 9,12-octadecadienoic acid; and in leaves, the coumarin derivative 4,4,6,8-tetramethyl-2-chromanone, vitamin E, phytol, and sitosterol. MIC values of 500 and 375 μg·mL−1 were obtained against E. amylovora for flower and leaf extracts, respectively, upon conjugation with chitosan oligomers (to improve solubility and bioavailability). In the case of E. vitivora, MIC values of 250 and 500 μg·mL−1, respectively, were registered. Regarding the antifungal activity, EC90 values of 975.8 and 603.5 μg·mL−1, respectively, were found. These findings suggest that H. syriacus (cv. ‘Mathilde’) may be a promising source of antimicrobials for agriculture

Antifungal activity of methylxanthines against grapevine trunk diseases

Methylxanthines, found in the seeds, leaves, and fruits of some plants, are receiving increasing attention as promising treatments for wood-degrading fungi. The aim of the study presented herein was to explore the potential applications of caffeine, four caffeine derivatives (viz. 8-bromo-caffeine, 8-iodo-caffeine, 8-(4-fluorophenoxy)-caffeine, and 8-(2, 3, 5, 6-tetrafluoroalcoxy)-caffeine), and theophylline as antifungals for Botryosphaeriaceae species associated with grapevine trunk diseases (GTDs). In vitro susceptibility tests were conducted to assess the antimycotic activity of the aforementioned compounds and their conjugated complexes with chitosan oligomers (COS). Caffeine, Br-caffeine, and I-caffeine exhibited higher efficacies than imidazole, the chosen antifungal control. Moreover, a strong synergistic behavior between COS and the methylxanthine derivatives was observed. The COS–I-caffeine complex showed the best overall performance against the phytopathogenic fungi with EC90 values of 471, 640, and 935 µg mL-1 for D. seriata, D. viticola, and N. parvum, respectively. In a second step, combinations of the new treatments with imidazole were also explored, resulting in further activity enhancement and EC90 values of 425, 271, and 509 mL-1 against D. seriata, D. viticola, and N. parvum, respectively, for the COS–I-caffeine-imidazole ternary compound. Given the high in vitro efficacy of these formulations for the control of GTDs, they may deserve further investigation with in vivo and field bioassays as an alternative to conventional fungicides. © 2022 by the authors. Licensee MDPI, Basel, Switzerland

Antifungal ativity against Botryosphaeriaceae fungi of the hydro-methanolic extract of Silybum marianum capitula conjugated with stevioside

Silybum marianum (L.) Gaertn, viz. milk thistle, has been the focus of research efforts in the past few years, albeit almost exclusively restricted to the medicinal properties of its fruits (achenes). Given that other milk thistle plant organs and tissues have been scarcely investigated for the presence of bioactive compounds, in this study, we present a phytochemical analysis of the extracts of S. marianum capitula during the flowering phenological stage (stage 67). Gas chromatography–mass spectroscopy results evidenced the presence of high contents of coniferyl alcohol (47.4%), and secondarily of ferulic acid ester, opening a new valorization strategy of this plant based on the former high-added-value component. Moreover, the application of the hydro-methanolic extracts as an antifungal agent has been also explored. Specifically, their activity against three fungal species responsible for the so-called Botryosphaeria dieback of grapevine (Neofusicoccum parvum, Dothiorella viticola and Diplodia seriata) has been assayed both in vitro and in vivo. From the mycelial growth inhibition assays, the best results (EC90 values of 303, 366, and 355 μg·mL−1 for N. parvum, D. viticola, and D. seriata, respectively) were not obtained for the hydroalcoholic extract alone, but after its conjugation with stevioside, which resulted in a strong synergistic behavior. Greenhouse experiments confirmed the efficacy of the conjugated complexes, pointing to the potential of the combination of milk thistle extracts with stevioside as a promising plant protection product in organic Viticulture