Surveys on Dothistroma spp. in France
In France, Dothistroma needle blight has been emerging over the last 15 years. Surveys were carried out in pine forest stands from 2007 to 2010 to better understand the distribution of the two pathogens that are associated with the disease: Dothistroma septosporum (teleomorph: Mycosphaerella pini - EU Annexes) and D. pini (teleomorph unknown), and to investigate whether the emergence of Dothistroma needle blight could be explained by a recent introduction of D. pini. Out of the 216 studied stands, D. septosporum and D. pini were detected in 133 and 123 stands, respectively. On 40 stands, both species were co-existing. Most infected samples were collected from P. nigra subsp. laricio, although some had been collected from P. nigra subsp. austriaca (9 samples), P. pinaster (4), and P. sylvestris (5). D. septosporum was detected in all pine species listed above, whereas D. pini was found only on Pinus nigra (subsp. laricio and austriaca). Results also showed that D. septosporum was evenly distributed across France, except in the Mediterranean area (rarely found along the Mediterranean Basin and absent from Corsica). D. pini showed a more restricted distribution, being very infrequent in Northern and Eastern France, as well as in the mountainous areas of the Massif Central and the Pyrénées. However, D. pini was widespread in Southern France. In addition to this field study, herbarium specimens were examined. Most of the specimens studied (21) were found to be infected by D. septosporum. D. pini was found in 2 specimens: 1 collected in 1907 at Tourbière du Beillard (Vosges), and 1 collected in 1965 at the Arboretum des Barres (Loiret). These rather old records suggest that the emergence of Dothistroma needle blight cannot be explained by a recent arrival of D. pini, but would probably be better explained by climate changes.
Sources
Fabre B, Ioos R, Piou D, Marçais B (2012) Is the emergence of Dothistroma needle blight of pine in France caused by the cryptic species Dothistroma pini? Phytopathology 102(1), 47-54.