Cytosporalongdensis sp. nov. and C.sinensis (Diaporthales, Valsaceae) associated with Populusalba subsp. pyramidalis canker and dieback in China.

Poplar is an important afforestation tree species globally and is widely cultivated in northern China. During a small-scale local disease survey in Ningxia, China, canker and dieback symptoms were observed in Populusalbasubsp.pyramidalis trees. The aim of this study was to identify the isolates associated with the symptoms observed and evaluate their pathogenicity on Populusalbasubsp.pyramidalis, Malusdomestica cv. 'Fuji' and Pyrusbretschneideri. Based on multi-gene phylogenetic analyses (ITS, act, rpb2, tef1-α, and tub2) and morphological comparisons, two Cytospora species were identified: C.sinensis and a novel species described here as C.longdensis sp. nov. Pathogenicity assays confirmed both species were pathogenic to Populusalbasubsp.pyramidalis, with C.sinensis exhibiting significantly stronger virulence than C.longdensis (p < 0.05). In contrast, their pathogenicity on Malusdomestica cv. 'Fuji' and Pyrusbretschneideri was negligible, indicating their host preference for Populusalbasubsp.pyramidalis. This study highlights the host-specific adaptation of Cytospora species and provides critical insights for managing Populusalbasubsp.pyramidalis canker and dieback diseases.