Comparative Analysis of Secondary Metabolites in Diplodia corticola Strains with Different Virulence Degrees Associated with Canker and Dieback of Quercus spp

Abstract

Diplodia corticola is one of the most aggressive fungal pathogens of Quercus species involved in the decline of Mediterranean oak forests. In this study, three strains of D. corticola associated with holm (Quercus ilex) and cork (Quercus suber) oak trees exhibiting dieback symptoms and cankers in Algeria were selected to investigate the production of secondary metabolites. Metabolomic analyses revealed the production of several known compounds, such as sphaeropsidins, diplopyrones and diplofuranones. Moreover, the comparative investigation of secondary metabolites produced by the analyzed strains with different degrees of virulence revealed possible implications of these compounds in the fungal virulence. In particular, sphaeropsidins seem to be the main phytotoxic compounds of D. corticola involved in the infections of Quercus species, with a possible synergistic influence of the less representative compounds in the fungal virulence.

Keywords: HPLC-ESI-HRMS; culture filtrates; mycelial extracts; quantitative analysis; sphaeropsidins; virulence factors.

Figure 1

Cork oak tree showing extensive twig and branch dieback (A); internal lesions of sectioned branches (B–E).

Figure 2

Lesion lengths (mm) caused by MAEC02, MAEC03 and MAEC10 strains of Diplodia corticola inoculated on detached green shoots of (A) Quercus ilex and (B) Quercus suber. Tests were performed in five replicates and results are presented as the mean ± standard deviation (SD). Data with different letters (a,b) in each panel are significantly different (one-way ANOVA followed by Tukey’s post hoc test; p < 0.05). Values with dissimilar letters are significantly different from each other (p < 0.05). Values with the same letter are not significantly different (p > 0.05).

Figure 3

Structures of metabolites detected in the culture filtrate (CE) and mycelial (ME) extracts of MAEC02, MAEC03 and MAEC10 strains of Diplodia corticola.

Figure 4

Concentrations (expressed as mg L⁻¹) of Sph A and Sph B in culture filtrates of Diplodia corticola MAEC02, MAEC03 and MAEC10. Analyses were performed in triplicate and results are presented as the mean ± standard deviation. Data with different letters (a,b) are significantly different (two-way ANOVA followed by Tukey’s post hoc test; p < 0.05). Values with dissimilar letters are significantly different from each other (p < 0.05). Values with the same letter are not significantly different (p > 0.05).