Abstract
Lignin-based nano- and microcarriers are a promising biodegradable drug delivery platform inside of plants. Many wood-decaying fungi are capable of degrading the wood component lignin by segregated lignases. These fungi are responsible for severe financial damage in agriculture, and many of these plant diseases cannot be treated today. However, enzymatic degradation is also an attractive handle to achieve a controlled release of drugs from artificial lignin vehicles. Herein, chemically cross-linked lignin nanocarriers (NCs) were prepared by aza-Michael addition in miniemulsion, followed by solvent evaporation. The cross-linking of lignin was achieved with the bio-based amines (spermine and spermidine). Several fungicides—namely, azoxystrobin, pyraclostrobin, tebuconazole, and boscalid—were encapsulated in situ during the miniemulsion polymerization, demonstrating the versatility of the method. Lignin NCs with diameters of 200–300 nm (determined by dynamic light scattering) were obtained, with high encapsulation efficiencies (70–99%, depending on the drug solubility). Lignin NCs successfully inhibited the growth of Phaeomoniella chlamydospora and Phaeoacremonium minimum, which are lignase-producing fungi associated with the worldwide occurring fungal grapevine trunk disease Esca. In planta studies proved their efficiency for at least 4 years after a single injection into Vitis vinifera (“Portugieser”) plants on a test vineyard in Germany. The lignin NCs are of high interest as biodegradable delivery vehicles to be applied by trunk injection against the devastating fungal disease Esca but might also be promising against other fungal plant diseases.
Highlights
Lignin has been recently investigated as a renewable, abundant, and inexpensive feedstock to develop sophisticated nanostructures.[1−3] Lignin is a highly cross-linked aromatic polyether−polyol that is separated from cellulose and hemicellulose during the pulping process in paper production
Lignin-based NCs with versatile drug-load were synthesized by aza-Michael cross-linking polymerization in miniemulsion of methacrylated lignin followed by solvent evaporation
Kraft lignin was submitted to chemical modification by esterification with methacrylic anhydride to produce lignin-MA with >90% of methacrylation estimated by 31P nuclear magnetic resonance (NMR)
Summary
Lignin has been recently investigated as a renewable, abundant, and inexpensive feedstock to develop sophisticated nanostructures.[1−3] Lignin is a highly cross-linked aromatic polyether−. Boscalid, azoxystrobin, and tebuconazole as a set of fungicides because of their high solubility in organic solvents and low solubility in water These fungicides are currently used in spraying applications in agriculture against different fungal diseases either alone or in mixed formulations due to their different modes of action (Figure S3 shows their chemical structures).[24,25] we studied the in vitro activity against fungi, related to the grapevine trunk disease Esca.[34,35]. Dose-dependent antifungal activities of NC formulations were compared to those of free fungicides by means of minimum inhibitory concentration (MIC) for a series of test microorganisms, all producing lignases: P. chlamydospore, Neonectria ditissima, Phytophtora infestans, Magnoporthe oryzae, Botrytis cinerea, Neofusicoccum parvum (Table 3) We studied both the pure fungicides (azoxystrobin, boscalid, pyraclostrobin, and tebuconazole) and the encapsulated fungicides (samples: AE02, BE01, PE02, TE02, and the mixture PE02/BE01). These data prove the versatility of the lignin encapsulation of various fungicides against Esca associated fungi
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