Diplodia Species Causing Dieback on Pinus Pinea: Relationship between Disease Incidence, Dendrometric and Ecological Parameters

Forest decline is a widespread phenomenon on coasts throughout the Mediterranean basin. Pathogenic fungi are amongst the main causes of forest tree diseases. Diplodia species, having a cosmopolitan distribution, are well-known as pathogens of woody plant hosts including Pinus spp. In recent years, symptoms of shoot dieback, necrosis, twig blight, canopy transparency and trunk cankers have been observed on Pinus pinea trees in Tunisian forests. Nevertheless, this has been less well-studied in North Africa and especially in Tunisia. The purpose of this study is to report the occurrence of Diplodia species causing dieback on P. pinea in two forests in northeastern and the northern Tunisia. A collection of fifty-eight isolates were obtained from symptomatic branches of P. pinea trees. Three Diplodia species were identified: D. africana, D. pseudoseriata and D. scrobiculata by means of morphological characteristics, and phylogenetic analysis. Their incidence on P. pinea trees appeared to be significantly correlated to the dendrometric parameters and ecological factors. A pathogenicity test was conducted on 3-years-old P. pinea seedlings, confirmed the virulence of three Diplodia species. Based on the length of vascular necrosis in the wood of the P. pinea inoculated stem, D. scrobiculata was the most virulent species. Data from the present study provide the first report of the species of Diplodia associated with P. pinea dieback in Tunisia.