Virulence of Cytospora chrysosperma (Pers.) Fr. Isolates on Walnut Seedlings and Excised Twigs

Cytospora dieback and canker disease is one of prevalent disease of walnut trees in Iran caused by several species of Cytospora genus. The aim of this study was to determination of virulence degree in 58 isolates of dominant species، Cytospora chrysosperma. isolates from 12 provinces of Iran; Hamedan، Kurdistan، Kermanshah، Ilam، West Azarbaijan، Zanjan، Markazi، Lorestan، Chaharmahal va Bakhtiari، Isfahan، Kohgilouye va Boyerahmad and Fars were inoculated on three-year old seedlings and lesion area have been recorded 30 days after inoculation. Furthermore، Pathogenicity survey on detached twigs carried out in laboratory situation to check accuracy of pathogenicity determination. Based on these results، there was noticeable variation in virulence degree of tested isolates. However، most of isolates didn’t show any pathogenicity. Indeed، 34% and 24% of isolates didn’t shown significant difference with control in pathogenicity test on seedlings and detached twigs، respectively. Also، there was week but significant (23%) correlation between two evaluation methods. Collectively، it seems that evaluation of virulence or resistance degree would not be reliable via the detached twigs technique.