The involvement of bark canker fungal pathogens in cypress windbreak dieback in northern Tunisia

Common cypress (Cupressus sempervirens L.) is a significant element in the Mediterranean region and Tunisia, present in both forest and agricultural windbreak for centuries. However, in recent decades, common cypresses in certain Tunisian areas have experienced dieback and mortality. Presently, many common cypress windbreaks display severe damage, possibly due to fungal pathogens. In the summer of 2022, a field survey was conducted in three regions of northern Tunisia (Menzel Bouzalfa, Morneg, El Alia) to investigate diseased common cypresses and identify the responsible pathogens: 935 trees belonging to 14 windbreaks were surveyed. Branches and twigs samples were collected from 47 affected trees showing symptoms such as yellowish-brown foliage, necrotic lesions, cankers, resin exudation and diebacks. Initially, isolates were morphologically characterized, and representative isolates were further analyzed using molecular methods. Using the traditional culture method, 41 fungal species associated with common cypress dieback were identified. Pathogenicity tests were performed on eight fungal species known as possible pathogens: Phaeobotryon cupressi, Diplodia cupressi, Diplodia olivarum, Diplodia pseudoseriata, Seiridium cardinale, Pestalotiopsis funereoides, Neofusicoccum mediterraneum, and Didymosphaeria variabile. Phaeobotryon cupressi, D. cupressi, and S. cardinale displayed the highest pathogenicity, followed by P. funereoides and D. olivarum, which caused smaller lesions. With the exception of D. cupressi, all of the identified fungal pathogens are being reported for the first time in Tunisia or in common cypress. The pathogenic action of most of the isolated fungi could have been enhanced by the prolonged droughts that have repeatedly occurred over recent years.