Phaeoacremonium species associated with olive wilt and decline in southern Italy

Six Phaeoacremonium species (spp.) were isolated from symptomatic wood of olive trees (Olea europea) in Apulia (southern Italy) that showed crown wilt and twig and branch dieback. These Phaeoacremonium spp. were identified according to their morphological characteristics and by analyses of partial sequences of the actin and beta-tubulin genes. Combining these cultural, morphological and molecular data, three Phaeoacremonium spp. were isolated that are already known to be responsible for severe decline of olive in Apulia, Phaeoacremonium aleophilum, Phaeoacremonium alvesii and Phaeoacremonium parasiticum, together with three other Phaeoacremonium spp. that are associated for the first time with wilt, decline and dieback of olive orchards in Italy and worldwide: Phaeoacremonium italicum, Phaeoacremonium sicilianum and Phaeoacremonium scolyti. To understand and to confirm their involvement in wilt and decline of olive trees, pathogenicity assays were performed on shoots of young olive plants. The data indicate that all six of these Phaeoacremonium spp. can cause discolouration, necrotic wood, and death of shoots, although different levels of virulence were observed, with Pm. italicum, Pm. aleophilum and Pm. sicilianum producing greater necrotic lesions than the other Phaeoacremonium spp. investigated here.