Morphological and molecular characterization of Cytospora species involved in apple decline in Iran

In a recent survey on apple orchards showing stem canker, dieback and decline symptoms in West Azerbayjan province, Iran, several fungal isolates with typical characteristics of the genus Cytospora were obtained. Combination of morphological and cultural characteristics and phylogenetic analysis of internal transcribed spacer region of the nrDNA (ITS-rDNA) and parts of large subunit of ribosomal DNA (LSU), actin (ACT) and RNA polymerase II (RPB2) genes were used to accurate delimitation of fungal species. Four Cytospora species viz. C. chrysosperma, C. germanica, C. paratranslucens and C. salicina were identified. Pathogenicity tests were conducted on detached branches of ‘Golden delicious’ and ‘Red delicious’ apple cultivars. Isolates of C. salicina caused characteristic lesions on both ‘Golden delicious’ and ‘Red delicious’ apple cultivars, while isolates of C. chrysosperma, C. germanica and C. paratranslucens were only pathogenic on ‘Red delicious’ apple cultivar. Re-isolation and identification of the inoculated fungi confirmed Koch’s postulates. This study indicated the presence of different Cytospora species causing apple canker, dieback and decline disease in the studied area. Cytospora germanica and C. salicina are reported for the first time as causal agents of apple canker disease. Moreover, these species are reported as new records for the mycobiota of Iran.