Cytospora longdensis sp. nov. and C. sinensis (Diaporthales, Valsaceae) associated with Populus alba 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, <i>Malusdomestica</i> cv. 'Fuji' and <i>Pyrusbretschneideri</i>. Based on multi-gene phylogenetic analyses (ITS, <i>act</i>, <i>rpb2</i>, <i>tef1-α</i>, and <i>tub2</i>) and morphological comparisons, two <i>Cytospora</i> species were identified: <i>C.sinensis</i> and a novel species described here as <i>C.longdensis</i> <b>sp. nov.</b> Pathogenicity assays confirmed both species were pathogenic to Populusalbasubsp.pyramidalis, with <i>C.sinensis</i> exhibiting significantly stronger virulence than <i>C.longdensis</i> (p < 0.05). In contrast, their pathogenicity on <i>Malusdomestica</i> cv. 'Fuji' and <i>Pyrusbretschneideri</i> was negligible, indicating their host preference for Populusalbasubsp.pyramidalis. This study highlights the host-specific adaptation of <i>Cytospora</i> species and provides critical insights for managing Populusalbasubsp.pyramidalis canker and dieback diseases.