Detection of fungal trunk pathogens from wood tissues and pruning wood debris of olive trees in Iran

Between April 2015 and August 2017 a survey was conducted in olive orchards in different regions in Iran in order to collect and identify fungal trunk pathogens. Wood samples were collected from the trunk and branches of olive trees showing dieback and cankers, as well as pruning wood debris left in the orchards. Fungal isolation was performed from necrotic woody tissues, as well as fruiting bodies observed on bark of wood debris. Morphological identification of the fungal isolates was confirmed by DNA sequencing and comparisons of the internal transcribed spacer (ITS) nrDNA region and a partial sequence of translation elongation factor 1-α (tef-1α) and β-tubulin (tub2) genes. In this study, eight species of Botryosphaeriaceae namely Botryosphaeria (B.) dothidea, Diplodia (D.) gallae, D. intermedia, D. mutila, Dothiorella (Do.) sarmentorum, Neofusicoccum (Neof.) parvum, Neoscytalidium (Neos.) dimidiatum (as the most abundant species) and Neos. novaehollandiae were identified. Moreover, Pleurostoma (Pl.) richardsiae, Paecilomyces (P.) formosus, a Coniophora-like fungus and several isolates of Phoma, Chaetomium, Darksidea and Hypoxylon species were obtained. Pathogenicity trials on detached shoots of olive trees conducted under greenhouse conditions showed that P. formosus, Neos. dimidiatum, D. gallae, Neof. parvum, Dot. sarmentorum, Neos. novaehollandiae, Pl. richardsiae, B. dothidea, D. mutila, D. intermedia and Coniophora-like fungus were pathogenic on inoculated olive shoots. Paecilomyces formosus was the most virulent and caused the longest lesions. Based on literature reviews, this study represents the first report on the occurrence of D. mutila, Neof. parvum and Pl. richardsiae from diseased olive trees in Iran. Moreover, this is the first report of D. gallae from fruiting bodies on the bark of branches, and four species (namely D. intermedia, Neos. novaehollandiae, P. formosus and Coniophora-like fungus) from affected olive trees worldwide. Our results provide new insights into the etiology of olive fungal trunk diseases.