Abstract
A severe branch dieback and canker was observed on black walnut (Juglans nigra L.) in Yili county, Xinjiang, China, during the spring and summer, 2016. A fungus was consistently isolated from infected branches. Pathogenicity tests showed that the fungus could infect branches, and produced the same symptoms under artificial inoculation conditions as those observed in the field. The fungus was identified based on morphological and cultural characteristics as Cytospora chrysosperma. Identification was confirmed by combining multi-locus phylogenetic analyses based on the internal transcribed spacer regions (ITS 1 and 2) and intervening 5.8S nrDNA, the partial translation elongation factor (TEF-1) gene, and partial gene regions of β-tubulin (TUB 2). Morphological and cultural characteristics, as well as the sequences of the ITS, tef and β-tubulin regions and pathogenicity tests, showed that the causal agent of the disease was C. chrysosperma. This is the first report of branch dieback and canker of black walnut caused by C. chrysosperma (Pers.) Fr. worldwide.
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