An outbreak of Cyclaneusma minus needle cast on Swiss mountain pine (Pinus uncinata) in Italy

In September 2010, a significant decline of Pinus uncinata was observed in a mixed forest of Larix decidua and P. cembra in Claviere (western Italian Alps). In the forest, which covered about 32 ha and was located between 1800 and 1900 m of elevation (coordinates: 44°56’05.19’’N - 6°45’28.46’’E), P. uncinata accounted for 12% of the trees. The disease affected 85-90% of P. uncinata trees belonging to all diameter classes. More than 70% of the trees showed needle yellowing, but the remaining trees showed thin and transparent crowns, and needle cast that progressed from the inner to the outer parts of the twigs. No symptoms were observed on L. decidua and P. cembra. Twenty symptomatic twigs were collected from 10 randomly selected trees. Needles were placed in Petri dishes containing a sterile piece of filter paper dampened with sterile water and incubated at room temperature for 10-12 days to induce sporulation. After incubation, white to creamy, scattered, elliptical apothecia embedded in yellowed needles were observed. Apothecia produced hyaline, filiform, 2- septate, smooth ascospores 80-90×2.5-3.0 μm in size. Based on these macro- and micro-morphological characters, the fungus was identified as Cyclaneusma minus (Butin) Di Cosmo, Peredo et Minter (syn. Naemacyclus minor Butin). C. minus has been reported both as an endophyte on symptomless P. uncinata needles (Sieber et al., 1999) and as a pathogen on needles of several pine species (Millar and Minter, 1980). In Italy, the fungus has previously been observed on Pinus sylvestris (Gonthier et al., 2010) but, to our knowledge, this is its first report on P. uncinata in this country.