Cytospora species associated with walnut canker disease in China, with description of a new species C. gigalocus

• It represents the first time to study this hot pathogen by multi-locus phylogeny.
• Three Cytospora species have been epitypified so as to further study in this taxa.
• A new species have been recorded from walnut tree using multi-phasic approach.
• Our results indicate a high species diversity of Cytospora causing walnut canker.
• Host affiliation is further proved not reliable for Cytospora species delimitation.

Cytospora species associated with canker disease are presently difficult to identify because of lack of ex-types cultures with molecular data, few distinguishable characters, and only Internal transcribed spacer (ITS) sequence data is available for most Cytospora strains in GenBank. We report on Cytospora species from the walnut tree in China. Collections were subjected to morphological and phylogenetic study. The relatedness of species associated with walnut canker were established using combined ITS, nrLSU, β-tubulin, and actin gene sequence data. Cytospora atrocirrhata, Cytospora chrysosperma, Cytospora sacculus, and a new species, Cytospora gigalocus, were identified causing canker disease of walnut. Cytospora gigalocus is formally described and compared with most similar species. Cytospora chrysosperma and C. sacculus have previously been recorded from walnut, whereas C. atrocirrhata is reported as associated with walnut canker for the first time. This is the first study that has established the Cytospora species causing walnut canker in China using a multi-phasic approach. All species are recorded as being associated with walnut canker disease in China for the first time.