Bark extract of Uncaria tomentosa L. for the control of strawberry phytopathogens

Abstract

Gray mold (<i>Botrytis cinerea</i> Pers.), crown and fruit rot (<i>Phytophthora cactorum</i> (Lebert and Cohn) J.Schröt), and verticillium wilt (<i>Verticillium dahliae</i> Kleb.) are among the main diseases that affect the strawberry crop. In the study presented herein, the bark extract of <i>Uncaria tomentosa</i> (Willd. ex Schult.) DC, popularly known as “cat’s claw”, has been evaluated for its capability to act as a sustainable control method. The bioactive compounds present in the aqueous ammonia extract were characterized by gas chromatography–mass spectroscopy, and the antimicrobial activity of the extract—alone and in combination with chitosan oligomers (COS)—was assessed in vitro and as a coating for postharvest treatment during storage. Octyl isobutyrate (30.7%), 19α methyl-2-oxoformosanan-16-carboxylate (9.3%), tetrahydro-2-methyl-thiophene (4.7%), and α-methyl manofuranoside (4.4%) were identified as the main phytoconstituents. The results of in vitro growth inhibition tests showed that, upon conjugation of the bark extract with COS, complete inhibition was reached at concentrations in the 39–93.75 μg∙mL⁻¹ range, depending on the pathogen. Concerning the effect of the treatment as a coating to prolong the storage life and control decay during post-harvest storage, high protection was observed at a concentration of 1000 μg∙mL⁻¹. Because of this effectiveness, higher than that attained with conventional synthetic fungicides, the bark extracts of cat’s claw may hold promise for strawberry crop protection.