Occurrence of twig blight and branch dieback of walnut caused by Botryosphaeriaceae species in Turkey

In the fall season 2017, forty samples showing necrotic and wilted leaves, stem cankers, shoot cankers, leaf and fruit blight were collected from walnut trees in seven commercial orchards in Aydin province of Turkey. Ten isolates were identified based on morphology of monoconidial cultures obtained from pine needles. Morphological characteristics and DNA sequence comparisons of ITS and EF-1 alpha gene sequences of the isolates revealed the presence of Botryosphaeria dothidea, Neofusicoccum parvum, and Neofusicoccum mediterraneum. Four isolates were identified as Neofusicoccum parvum with 100% similarity for ITS (accession nos. MW426289 to MW426292) and EF1 alpha (MT212730 to MT212733); two isolates were Neofusicoccum mediterraneum with 100% similarity for ITS (accession nos. MW426287 and MW426288) and EF1 alpha (MT212728 and MT21729), and one isolate was Botryosphaeria dothidea with 100% similarity for ITS (accession nos. MW426293) and EF1 alpha (MT212734). Pathogenicity tests were conducted on 2-year-old walnut trees cv. Chandler, and ten monoconidial isolates were pathogenic. This is the first report of N. parvum and B. dothidea causing twig blight and branch and dieback disease of walnuts in the Aegean region of Turkey and N. mediterraneum on walnut trees in Turkey. This emerging disease could pose a potential threat to new tree plantations of walnut in Turkey.

Automated summary

In this study, walnut samples were collected from seven commercial orchards in Aydin province of Turkey and identified three fungal species (Botryosphaeria dothidea, Neofusicoccum parvum, and Neofusicoccum mediterraneum) causing diseases in walnut trees. These diseases could pose a potential threat to new tree plantations of walnut in Turkey.