Antagonistic behaviour of Phaeomoniella sp. and Phaeocremonium spp vs. Fomitiporia mediterranea: Isolation, purification, chemical and biological characterization of active compounds

The recent advancement made by the research on "esca" of grapevine has contributed to shed light upon the aetiology and pathogenesis of this disease complex. The pathogenic ability of the three fungi most commonly associated with the disease, i.e. the thracheiphilous hyphomycetes Phaeomoniella chlamydospora (Pch) and Phaeoacremonium aleophilum (Pal) and the wood-rotting basidiomycete Fomitiporia mediterranea (Fme) was clearly demonstrated. The non-synergistic, competitive association of the two hyphomycetes and the inhibition of Fme growth were depicted. The objectives of this study were to: 1. assess the toxigenicity of P. angustius (Pan), P. inflatipes (Pin), P. parasiticum (Ppa), P. rubrigenum (Pru), P. viticola (Pvi) and their growth inhibition activity vs. Fme; 2. study on how Pch, Pal and Fme interact each other and with the host tissue; 3. isolate and characterise chemically and biologically the substances involved in how the mycelium of each fungus functions and how the fungi co-ordinate their activities. The culture filtrates of all strains, assayed on detached leaves of ‘Italia’ or 'Sangiovese' grapevines, resulted phytotoxic. Isosclerone was produced by Pal, Pch, Pin, Pan, Pru, Pvi, whereas scytalone was produced by Pal, Pch, Pin, Pan and Ppa. Pullulan was also produced by Pan, Pin, Ppa and Pvi. In dual cultures, the antagonism vs. Fme was clearly shown on malt-agar plates: the margin of the Fme colonies turned brown, became thicker, and aerial hyphae formed a ridge-like barrier between the two fungi. This experiment showed that the antagonistic effect vs. Fme was probably due to the production by the strains of Phaeoacremonium spp. and Pch of substances that spread through the medium and affected the Fme colony. All Phaeoacremonium spp. and Pch strains were used for the concentration and desalting of culture filtrates through an anisotropic membrane. Most of the growth inhibitor activity of the crude culture filtrate was located in the 3-10 kDa or up to 3 kDa fractions. These fractions were found to contain peptides and proteins with suppressive effect on Fme growth.