During a survey conducted in August 2009 in northern Norway, symptoms typical for red band needle blight (1) were observed in four young Scots pine (Pinus sylvestris) stands. The stands, less than 15 years old, were located in humid sites near rivers in Bardu and Målselv municipalities, Troms County. Many of the oldest needles (2- to 3-years-old) in the lower part of young trees were partially or completely brown, but still attached, and red bands could be observed. Aggregations of conidial stromata were often seen in the red bands. Conidia were hyaline, smooth, thin walled, and filiform, 1.9 to 2.6 μm wide and 12 to 36 μm long. Isolations were made from conidiomata and the identity of Mycosphaerella pini was confirmed by partial sequencing of the internal transcribed spacer (ITS) region of a sample from Målselv (69°00′N, 18°51′E) (GenBank Accession No. JF796109). In June 2010, a survey was done in southeastern Norway where nearly 100 stands with young Scots pine, up to 20 years old, were inspected and typical symptoms of red band needle blight were observed in 10 stands in three municipalities in Hedmark County (Eidskog, Kongsvinger, and Trysil), less than 25 km from the Swedish border, and in one stand in Buskerud County (Nedre Eiker). Lower branches of up to 5 m tall trees had symptoms of red band needle blight, mainly on the oldest needles. In the red bands, acervuli of Dothistroma septosporum, the anamorph of M. pini, appeared. Typical conidia from acervuli were germinated in water agar and resulting mycelium was transferred to modified orange serum agar. Two isolates were sequenced as above and both herbarium samples and isolates (Kongsvinger, 60°06′N, 12°04′E; GenBank Accession No. JF796108 and Trysil, 61°14′N, 12°22′E; GenBank Accession No. JF796107) were deposited at the Norwegian Forest and Landscape Institute. To fulfill Koch's postulates, symptoms were reproduced by artificial inoculation onto 1-year-old Scots pine seedlings. In June 2010, a pooled conidial suspension (2.4 to 3.8 × 103 conidia per ml) from two single-conidium cultures was sprayed to runoff onto 128 seedlings and 64 seedlings were mock sprayed with distilled water. First symptoms (brown segments and red bands) appeared on inoculated seedlings 1 month later and acervuli appeared after another 6 to 8 weeks. M. pini was reisolated from the acervuli. Three months after inoculation, 90% of inoculated seedlings showed symptoms while all uninoculated seedlings were healthy. Damage caused by M. pini has increased in the northern hemisphere during the last 15 to 20 years, possibly because of climate change (4). In 2006, the fungus was recorded in Estonia (2), in 2008 in Finland (3), and by 2009, the disease had spread over large areas in Finland including the region near the Norwegian border in the north. The disease has been in Sweden for a few years (J. Stenlid, personnel communication). In southern Norway, the disease has mainly been observed near the Swedish border so here the disease may originate from Sweden. So far, however, only small areas of Norway have been surveyed. Both natural spread and human transport dissemination may be occurring.
References: (1) Anonymous. OEPP/EPPO Bull. 35, 303, 2005. (2) M. Hanso and R. Drenkhan. Plant Pathol. 57:170, 2008. (3) M. Müller et al. Plant Dis. 93:322, 2009. (4) A. Woods et al. BioScience 55:761, 2005.