Physicochemical Characterization and Antimicrobial Activity against Erwinia amylovora, Erwinia vitivora, and Diplodia seriata of a Light Purple Hibiscus syriacus L. Cultivar

Abstract

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.

Valorization of Quercus suber L. Bark as a Source of Phytochemicals with Antimicrobial Activity against Apple Tree Diseases

“…Regarding antibacterial activity, the inhibition results against E. amylovora would be comparable to those obtained by Fontana et al [71] for the hydroethanolic, methanolic, and maltodextrin-conjugated extracts of Moringa oleifera Lam. leaves, with MIC values of 1000 µg•mL −1 ; and with those obtained for hydromethanolic extracts of P. granatum fruits [72], of flowers or leaves of Hibiscus syriacus L. [73], and of flowers or leaves of Limonium binervosum (G.E.Sm.) C.E.…”

Bark Extract of Uncaria tomentosa L. for the Control of Strawberry Phytopathogens

“…In relation to the activity of COS, it is well established and may be ascribed to several mechanisms of action [37], including increased permeability of plasma membrane and the leakage of cellular contents, deprivation of trace elements essential for fungal normal growth due to its chelating action, and inhibition of mRNA synthesis and affection of protein and enzyme production due to binding to fungal DNA. As for the mechanism behind the high SFs observed for the conjugate complexes, synergism between COS and plant extracts may be explained by the fact that fungal pathogens are not resistant to multiple fungitoxicants [38], although solubility and bioavailability enhancements associated with conjugation have also been advocated in other works [39,40].…”

Phytochemical Profiling of Sambucus nigra L. Flower and Leaf Extracts and Their Antimicrobial Potential against Almond Tree Pathogens

“…In particular, the flavonoid named 4H-pyran-4-one, 2,3-dihydro-3,5-dihydroxy-6-methyl- (or 3,5-dihydroxy-6-methyl-2,3-dihydropyran-4-one) has been isolated from Chuanminshen violaceum Sheh and Shan (25%) [ 30 ], Punica granatum var. nana L. (9.7%) [ 31 ], Nephrolepis biserrata (Sw.) Schott (9.3%) [ 32 ], Hibiscus syriacus L. (4.2%) [ 33 ], Cyperus rotundus L. (3.8%) [ 34 ], Euphorbia serrata L., Camellia japonica L., Acalypha indica L., Ammannia baccifera L., Borassus flabellifer L., Cocculus hirsutus (L.) Diels, Cucumis sativus L., Leucas aspera (Willd.) Link, Litchi chinensis Sonn., Marsilea quadrifolia L., and Rumex vesicarius L. [ 35 ].…”