Characterization and pathogenicity of Neoscytalidium novaehollandiae causing dieback and sooty canker in Iran

Members of the Botryosphaeriaceae commonly cause stem cankers and dieback of tropical and subtropical woody plants. A survey was conducted to isolate and identify the fungal causal agents of dieback and sooty canker of trees in some areas of Khuzestan province, southwestern Iran, 2015–2022. Following visual inspection, 63 trees belonging to 22 species were detected with typical signs of the disease in eight townships, and symptomatic material including branches and stems were sampled from those trees. Fungal isolation was performed on Potato Dextrose Agar (PDA), and the isolates obtained were induced into sporulation using pine needles in Water Agar (WA). All isolates were identified as Neoscytalidium novaehollandiae, based on multi-gene phylogenetic analyses of combined ITS, LSU, and tef-1α sequence data, in combination with morphological comparisons. In a pathogenicity trial, five representative strains of N. novaehollandiae were inoculated onto healthy stem fragments from their respective original host tree species, resulting in severe necrotic lesions in all cases. Field assessment of sooty canker and dieback of trees in areas under investigation showed that at least 5–30 percent of ornamental and fruit trees were affected by N. novaehollandiae , with disease severity of 11.1 to 28.2 percent. Ficus benghalensis , Morus nigra , Juglans regia and Eucalyptus camaldulensis trees were more frequently and severely affected, as compared to Cassia fistula and Syzygium cumini . This study reports 22 new hosts for N. novaehollandiae in association with serious disease symptoms in Iran.