Biostimulant activity of hydrolyzable tannins from sweet chestnut (Castanea sativa Mill.)

Sweet Chestnut raw extracts, high in hydrolyzable tannins, hot water-extracted from untreated wood and reverse osmosis-concentrated, have presently several industrial and agricultural uses, the latter as fertilizer ingredients and a feed supplement. As a starter treatment, they proved to boost early plant growth, rooting, and phosphate uptake, and enhance plant resistance to nematodes, representing a natural alternative in agrochemical, residue-free crop products, and agro-environmental-oriented crop programs. To formulate more use-oriented products, several whole water extracts and process streams, obtained by membrane separation technology, were analyzed and characterized. The properties of the extracts, streams, and selected fraction mixtures were evaluated as biostimulants. Improved formulations of standardized tannin fractions had more consistent positive effects on plant resistance to biotic stress, and particularly nematodes. Fraction mixtures for direct spraying on crops, to inhibit some biochemical-related spoiling processes, and improve safety and quality of plant products, are presently patent pending for reducing TSNA in tobacco leaf.