Antifungal Agents Based on Chitosan Oligomers, ε-polylysine and Streptomyces spp. Secondary Metabolites against Three Botryosphaeriaceae Species

Abstract

Grapevine trunk diseases (GTDs) are a major threat to the wine and grape industry. The aim of the study was to investigate the antifungal activity against Neofusicoccum parvum, Diplodia seriata, and Botryosphaeria dothidea of ε-polylysine, chitosan oligomers, their conjugates, Streptomyces rochei and S. lavendofoliae culture filtrates, and their binary mixtures with chitosan oligomers. In vitro mycelial growth inhibition tests suggest that the efficacy of these treatments, in particular those based on ε-polylysine and ε-polylysine:chitosan oligomers 1:1 w/w conjugate, against the three Botryosphaeriaceae species would be comparable to or higher than that of conventional synthetic fungicides. In the case of ε-polylysine, EC₉₀ values as low as 227, 26.9, and 22.5 µg·mL^-1 were obtained for N. parvum, D. seriata, and B. dothidea, respectively. Although the efficacy of the conjugate was slightly lower, with EC₉₀ values of 507.5, 580.2, and 497.4 µg·mL^-1, respectively, it may represent a more cost-effective option to the utilization of pure ε-polylysine. The proposed treatments may offer a viable and sustainable alternative for controlling GTDs.

Keywords: Botryosphaeria dothidea; Diplodia seriata; Neofusicoccum parvum; conjugate complexes; grapevine trunk diseases.

Figure 1

Comparison of the attenuated total reflection (ATR)-Fourier-Transform Infrared (FTIR) spectra of ε-polylysine:chitosan oligomers conjugates prepared with different ε-polylysine:chitosan oligomers mass ratios. Only the fingerprint region is shown.

Figure 2

N. parvum mycelial growth inhibition assays for: (a) chitosan oligomers; (b) ε-polylysine; (c) S. rochei secondary metabolites; (d) S. lavendofoliae secondary metabolites; (e) ε-polylysine:chitosan (1:1 w/w) conjugates; (f) S. rochei secondary metabolites + chitosan oligomers (1:1 w/w); and (g) S. lavendofoliae secondary metabolites + chitosan oligomers (1:1 w/w). The concentration of the treatments decreases from top to bottom (doses for each treatment are indicated in Table 3). The petri dish in the bottom right corner shows the PDA control. Only one replicate per each treatment and dose is shown.

Figure 3

Radial growth values of (a) N. parvum; (b) D. seriata; and (c) B. dothidea in the presence of the different treatments under study at different concentrations (in µg·mL⁻¹). COS, EPL, MR, ML and C stand for chitosan oligomers, ε-polylysine, S. rochei secondary metabolites, S. lavendofoliae secondary metabolites and control, respectively. For MR and ML only one column is shown, since no inhibition was detected at any concentration in the 250–1500 µg·mL⁻¹ range. Concentrations labelled with the same uppercase letters are not significantly different at p < 0.05 by Tukey’s test. All values are presented as the average of three repetitions. Error bars represent the standard deviation across three replicates.