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

Abstract

Gray mold (Botrytis cinerea Pers.), crown and fruit rot (Phytophthora cactorum (Lebert and Cohn) J.Schröt), and verticillium wilt (Verticillium dahliae Kleb.) are among the main diseases that affect the strawberry crop. In the study presented herein, the bark extract of Uncaria tomentosa (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.

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

“…As for V. dahliae , many more plant-derived products have been tested in the literature. The MIC values reported herein for S. nigra extracts (984 and 975 µg·mL −1 ) would be approximately twice those of U. tomentosa [ 26 ] and Chrysanthemum coronarium L. [ 56 ] extracts; would be comparable to the one reported for Haplophyllum tuberculatum (Forssk.) Juss.…”

“…An aqueous ammonia solution was chosen to dissolve the bioactive compounds of interest. The flower extract was prepared according to the procedure described in [ 26 ]: the flowers powder (30 g) was first digested in an aqueous ammonia solution (140 mL H 2 O + 10 mL NH 3 ) for 2 h, then sonicated in pulsed mode (with a 2 min stop every 2.5 min) for 10 min using a probe-type ultrasonicator (model UIP1000hdT; 1000 W, 20 kHz; Hielscher Ultrasonics, Teltow, Germany), and then allowed to stand for 24 h. It was then adjusted to neutral pH using acetic acid. Finally, the solution was centrifuged at 9000 rpm for 15 min, and the supernatant was filtered through Whatman No.…”

Holm Oak (Quercus ilex subsp. ballota (Desf.) Samp.) Bark Aqueous Ammonia Extract for the Control of Invasive Forest Pathogens

“…An aqueous ammonia solution was chosen to dissolve the bioactive compounds of interest contained in the bark of holm oak. The bark extract was prepared according to the procedure described in [ 60 ]. Briefly stated, a probe-type ultrasonicator (model UIP1000hdT; 1000 W, 20 kHz; Hielscher Ultrasonics, Teltow, Germany) was used to sonicate the bark sample for 10 min in pulse mode with a 2 min break after every 2.5 min of sonication, and the sample was then left to settle for 24 h. Acetic acid was then used to change the pH to neutral.…”

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

“…Concerning P. cactorum, the commercial CUSTOS TM formulated Allium-based extract (MIC = 100 µg•mL −1 ) [67], ethanolic extracts of Pinus spp. (MIC = 100 µg•mL −1 ) [68], and the aqueous ammonia extract of U. tomentosa bark (MIC = 187.5 µg•mL −1 ) [30] would be more effective than the Q. suber bark extract and its conjugate presented herein (with MIC values of 750 and 375 µg•mL −1 , respectively). On the other hand, commercial essential oils were minimally effective in the inhibition of this oomycete [69,70].…”

“…The preparation of the Q. suber bark extract followed the method previously described in [30]; briefly, the bark powder sample was first digested in an aqueous ammonia solution for 2 h, then sonicated in pulsed mode (with a 2 min stop every 2.5 min) for 10 min using a probe-type ultrasonicator (model UIP1000hdT; 1000 W, 20 kHz; Hielscher Ultrasonics, Teltow, Germany), and then allowed to stand for 24 h. Finally, the solution was centrifuged at 9000 rpm for 15 min, and the supernatant was filtered through Whatman No. 1 paper.…”