Botryosphaeriaceae species associated with lentisk dieback in Italy and description of Diplodia insularis sp nov.

Lentisk (Pistacia lentiscus L.) is an evergreen shrub that is widespread throughout the Mediterranean region. Since spring 2012, a severe and unusual disease of unknown aetiology has been observed on lentisk in six islands of the La Maddalena archipelago (Italy). The affected plants showed leaf chlorosis, crown thinning, branch dieback and sunken cankers. When branches with sunken cankers were cross-sectioned, internal wood symptoms included characteristic V-shaped necrotic sectors. Frequently, the necrotic lesions girdled the branches resulting in death of the upper crowns. Since there is no information about the aetiology of this disease and given the high ecological importance of these natural ecosystems, from spring 2012 to summer 2014, 37 samples of twigs and branches of lentisk showing sunken cankers were collected and processed. Symptomatic woody samples yielded fungal isolates representing two distinct genera in the Botryosphaeriaceae. On the basis of morphological features and DNA sequence data three distinct species: Diplodia olivarum, Neofusicoccum cryptoaustrale and N. luteum were identified. In addition, another Diplodia species morphologically distinct from all known species was isolated. Phylogenetic analyses based on nucleotide sequences of ITS and tef1-alpha regions showed that this new Diplodia species is most closely related to D. pseudoseriata and D. alatafructa. Pathogenicity trials carried out in field conditions on asymptomatic branches of lentisk showed that all four species are aggressive pathogens on this host and therefore directly involved in the severe dieback that is currently threatening this typical shrub of the Mediterranean maquis.