Mycelial compatibility of 62 isolates ofValsa malicolafrom different hosts and areas of Iran were investigated on potato dextrose agar (PDA) and oat meal agar (OMA). Four mycelial compatibility groups (MCGs) on PDA, 1–4, including three single membered (1–3) and a 58 membered (4) were identified. However, 8 MCGs, 1–8, consisting of 6 single membered (1–3, 5, 6 and 8), a 6 membered (4) and a 50 membered (7) were identified on OMA. On PDA, the number of groups and the time to achieve results were less than on OMA as well as the barrage zones were clearer on PDA than OMA. There was no correlation between groups and host or geographical origins of the isolates. The low number of identified MCGs on both culture media revealed low genetic diversity of investigated isolates ofV. malicola. [ABSTRACT FROM AUTHOR]