Characterization of Fusarium nirenbergiae and F. elaeidis causing diseases on Dipladenia and Grevillea plants

During 2019, severe symptoms of crown, basal stem and root rot associated with vascular discoloration were observed on Dipladenia and Grevillea ornamental species in a nursery located in Southern Italy. Fusarium spp. colonies were consistently recovered from infected tissues on semi-selective media. Molecular and phylogenetic analyses of the internal transcribed spacer (ITS) of rDNA, RNA polymerase second largest subunit (RPB2) and elongation factor 1-alpha (tef1-α) regions allowed to identify F. nirenbergiae and F. elaeidis as causal agents of infections from Dipladenia Sundaville® and Grevillea gracilis, respectively. The pathogenicity of both fungi was confirmed on young pot-grown cuttings of two ornamental plants, where they reproduced symptoms very similar to those observed in the nursery. Re-isolation of fungi from symptomatic tissues definitively confirmed aetiology of infections. In addition, among tested Dipladenia cultivars, “Classic Red” showed the significant highest percentage of disease incidence (almost 40% of plants) one month post inoculation. Similarly, disease occurrence recorded on young cuttings G. gracilis reached the maximum level 20 days after inoculation, interesting 100% of plants. This study reports the occurrence of Fusarium nirenbergiae and F. elaeidis causing diseases on Dipladenia and Grevillea plants.