Antifungal Activity of Chitosan Oligomers–Amino Acid Conjugate Complexes against Fusarium culmorum in Spelt (Triticum spelta L.)

Abstract

Fusarium head blight (FHB) is a complex disease of cereals caused by Fusarium species, which causes severe damages in terms of yield quality and quantity worldwide, and which produces mycotoxin contamination, posing a serious threat to public health. In the study presented herein, the antifungal activity against Fusarium culmorum of chitosan oligomers (COS)–amino acid conjugate complexes was investigated both in vitro and in vivo. The amino acids assayed were cysteine, glycine, proline and tyrosine. In vitro tests showed an enhancement of mycelial growth inhibition, with EC50 and EC90 effective concentration values ranging from 320 to 948 µg·mL−1 and from 1107 to 1407 µg·mL−1 respectively, for the conjugate complexes, as a result of the synergistic behavior between COS and the amino acids, tentatively ascribed to enhanced cell membrane damage originating from lipid peroxidation. Tests on colonies showed a maximum percentage reduction in the number of colonies at 1500 µg·mL−1 concentration, while grain tests were found to inhibit fungal growth, reducing deoxynivalenol content by 89%. The formulation that showed the best performance, i.e., the conjugate complex based on COS and tyrosine, was further investigated in a small-scale field trial with artificially inoculated spelt (Triticum spelta L.), and as a seed treatment to inhibit fungal growth in spelt seedlings. The field experiment showed that the chosen formulation induced a decrease in disease severity, with a control efficacy of 83.5%, while the seed tests showed that the treatment did not affect the percentage of germination and resulted in a lower incidence of root rot caused by the pathogen, albeit with a lower control efficacy (50%). Consequently, the reported conjugate complexes hold enough promise for crop protection applications to deserve further examination in larger field trials, with other Fusarium spp. pathogens and/or Triticum species.

On the Applicability of Chitosan Oligomers-Amino Acid Conjugate Complexes as Eco-Friendly Fungicides against Grapevine Trunk Pathogens

“…The EC 90 values attained with a COS−ε-polylysine conjugate (507.5, 580.2 and 497.4 µg•mL −1 for N. parvum, D. seriata and B. dothidea, respectively [33]) were better than those attained in this work for the COS−Tyr conjugate (1021.4, 672.1 and 707.7 µg•mL −1 , respectively), but-from an economic perspective-the latter formulation would be much more viable (given that the price of ε-polylysine is much higher than that of tyrosine: 245 €/100 mg vs. 58 €/100 g). An additional advantage of the COS-Tyr formulation could be its versatility as a crop protection product: EC 50 and EC 90 values against Fusarium culmorum (320 and 1107 µg•mL −1 , respectively) were of the same order of magnitude as those reported herein [37].…”

“…As regards the mode of action of the conjugate complex, it may be the result of an enhanced additive fungicidal effect per se, and/or via a concurrent action on diverse fungal metabolic sites. In a previous work [37], we also hypothesized that conjugation of COS and Tyr increases the cationic surface charge of COS, enhancing the linkage (through electrostatic interactions) to the negatively charged site-specific binding receptors on the fungal membrane.…”

Characterization and Antimicrobial Activity of a Halophyte from the Asturian Coast (Spain): Limonium binervosum (G.E.Sm.) C.E.Salmon

“…Nonetheless, it was suggested that it might be the result of an enhanced additive antimicrobial effect, per se, and/or via a concurrent action on diverse microbial metabolic sites. An increase in the cationic surface charge of COS may also result from conjugation with phytochemicals, which would enhance the linkage to negatively charged site-specific binding receptors on the bacterial/fungal membranes [ 70 , 71 , 72 , 73 ].…”

Physicochemical Characterization of Crithmum maritimum L. and Daucus carota subsp. gummifer (Syme) Hook.fil. and Their Antimicrobial Activity against Apple Tree and Grapevine Phytopathogens

“…It has been hypothesized that it may be the result of an enhanced additive fungicidal effect per se, and/or via a concurrent action on diverse fungal metabolic sites. The conjugation with phytochemicals may increase the cationic surface charge of COS, enhancing the linkage (through electrostatic interactions) to the negatively charged site-specific binding receptors on the fungal membrane [28,[64][65][66].…”