Cytospora species associated with apple canker and dieback disease in Iran with the description of three new species

Cytospora species are important plant pathogens causing destructive canker and die-back diseases on numerous host plants worldwide. Accurate species identification in the genus Cytospora is difficult and requires a combination of morphological characteristics and sequence data from multi-genomic regions. This study examined the diversity of Cytospora species associated with canker, die-back, and decline disease of apple trees in West Azarbaijan province, Iran. A total of 38 strains were isolated and obtained in pure culture. Based on morphological observation and multi-gene phylogenetic analyses (ITS, LSU, ACT, and RPB2), they were identified as five species—Cytospora mali-domesticae sp. nov., C. michailidesiana sp. nov., C. miyandoabensis sp. nov., C. longiostiolata, and C. parasitica. Pathogenicity tests were conducted on 1–2-year-old shoots of “Golden Delicious” and “Red Delicious” apple cultivars in the laboratory. Discoloration of bark and wood of inoculated shoots and re-isolation/re-identification of inoculated isolates confirmed Koch’s postulates. Apple is a new host (matrix nova) for C. longiostiolata, and this species represents a new record for the mycobiota of Asia. The results of this study provide valuable information on the diversity of Cytospora species associated with apple trees with canker, die-back, and decline disease in Iran and could assist in formulating ongoing disease management strategies.