Sydowia polyspora associated with current season needle necrosis (CSNN) on Pinus brutia Ten. in Türkiye

Abstract

Sydowia polyspora is a common fungal species living on conifers, often occurring as an epiphyte or endophyte on asymptomatic plants and in seeds. The fungus may become pathogenic under abiotic or biotic stress conditions. It is often associated with current season needle necrosis and shoot dieback on conifer species, especially Abies spp. and Pinus spp. throughout Europe and North America. The conifer Pinus brutia is common and widely distributed in Türkiye and is frequently used in reforestation. The work described here aimed to investigate the S. polyspora associated with needle necrosis and shoot dieback in five different Pinus brutia stands located in Denizli-Türkiye, to determine the severity of the disease and to reveal the pathogenicity of this agent in P. brutia seedlings. For this purpose, fungal isolations from symptomatic P. brutia needles were carried out in five different stands. In total, 68 S. polyspora isolates were obtained, each from a different tree from which macroscopic-microscopic morphological characterization was made and molecular characterization was done using the internal transcribed spacer (ITS) region. BLAST analysis of the ITS sequences confirmed the identification of the isolates, with 99–100% similarity to previously reported sequences of S. polyspora. Disease incidence and severity were assessed in five P. brutia stands. The disease incidence ranged between 38% and 62% (mean = 47%) while disease severity varied among sites. Pathogenicity studies were carried out on 2-year-old P. brutia seedlings using obtained isolates. Infection frequency in inoculated shoots was 90%. The pathogenicity tests, followed by re-isolation of the fungus from symptomatic shoots clearly demonstrated that S. polyspora played a role in the development of needle necrosis and shoot dieback in P. brutia stands. To the best of our knowledge, this is the first report of current season needle necrosis and shoot dieback on P. brutia caused by S. polyspora in Türkiye.