Identification and Characterization of Neocosmospora silvicola Causing Canker Disease on Pinus armandii in China

Chinese white pine, Pinus armandii, is a source of high-quality timber and an afforestation tree in China, which plays an important ecological and social role in water and soil conservation. Recently, a new canker disease has been reported in Longnan City, Gansu Province, where P. armandii is mainly distributed. In this study, the causal agent was isolated from diseased samples and identified as a fungal pathogen, Neocosmospora silvicola, based on morphological characteristics and molecular analyses (internal transcribed spacer, large subunit, RNA polymerase II, and translation elongation factor-1α). Pathogenicity tests on P. armandii revealed that N. silvicola isolates caused a 60% average mortality rate in artificially inoculated 2-year-old seedlings. The pathogenicity of these isolates was also observed on the branches of 10-year-old P. armandii trees with a 100% mortality rate. These results agree with the isolation of N. silvicola from diseased plants, suggesting the possible role of this fungus in the decline of P. armandii plants. Mycelial growth of N. silvicola was fastest on potato dextrose agar medium, and growth occurred at pH values ranging from 4.0 to 11.0 with temperatures between 5 and 40°C. The fungus also grew rapidly in complete darkness compared with other light conditions. Of the eight carbon and seven nitrogen sources tested, starch and sodium nitrate, respectively, were highly efficient in supporting the mycelial growth of N. silvicola. The ability of N. silvicola to grow at low temperatures (5°C) may explain its occurrence in the Longnan area of Gansu Province. This article is the first report of N. silvicola as an important fungal pathogen causing branch and stem cankers on Pinus tree species, which remains a threat to the forests.