Metabolites produced by agents of dieback of grapevine in Sicily: Lasiodiplodia mediterranea, Neofusicoccum parvum and N. vitifusiforme

Botryosphaeria dieback was recently reported in West Sicilian vineyards. The disease complex was only associated with isolates of genus Lasiodiplodia in 2007 and together with Diplodia seriata, Neofusicoccum parvum and Neofusicoccum vitifusiforme, this latest reported for the first time on Vitis vinifera in Italy. Moreover, a representative isolate of each species was inoculated on green shoots and fulfilled Koch’s postulates, although the lengths of vascular discolourations were variable depending on the species. As well as the other GTD causal agents, the expression of foliar symptoms (pale colour along the margins and between veins) was also occasional in Sicily, it was hypothesized that leaf symptoms could be due to fungal toxins, being produced in the woody tissues and translocated to the leaves through the transpiration streams. In order to improve the knowledge on host-pathogen interactions of the fungi associated with Botryosphaeria dieback, a study was undertaken of the pathogenicity of Sicilian botryosphaeriaceous fungi and their ability to produce phytotoxins. Artificial inoculations in planta confirmed the pathogenicity of all tested isolates. In addition, a strain of Lasiodiplodia mediterranea produced several metabolites in liquid medium. Among these, two new dimeric γ-lactols, lasiolactols A and B were characterized by 1D- and 2D-NMR and HR-ESI-MS, and another four metabolites were identified as botryosphaeriodiplodin, (5R)-5-hydroxylasiodiplodin, (-)-(1R,2R)-jasmonic acid, (-)-(3S,4R,5R)-4-hydroxymethyl-3,5-dimethyldihydro-2-furanone. The tested compounds at different concentrations (0.125, 0.25, 0.5 and 1 mg mL-1) on grapevine cv. Inzolia leaves were phytotoxic: among these, jasmonic acid showed the greatest toxicity. All metabolites did not show in vitro antifungal activity against four phytopathogens. Moreover, some lipophilic low molecular weight metabolites were isolated from N. parvum and N. vitifusiforme culture filtrates. Preliminary spectroscopic investigation showed that two strains produced metabolites belonging to different classes of natural compounds. In particular, some naphthalenone polyketides were isolated from organic extracts of N. parvum. The chemical and biological characterization of all metabolites is now in progress.