Morphological and Molecular Identification of Dactylonectria macrodidyma as Causal Agent of a Severe Prunus lusitanica Dieback in Italy

During the summer of 2016, severe dieback was observed on young potted Prunus lusitanica (Portugal laurel) plants in a nursery Pistoia province (Tuscany, Italy). Cylindrocarpon-like isolates were consistently recovered from diseased plant tissues. The combination morphological and molecular traits, including sequence data histone 3 β-tubulin genes (HIS3, TUB2) internal transcribed spacers (ITS), allowed identification Dactylonectria macrodidyma (Halleen, Schroers & Crous) L. Lombard Crous (asexual form Cylindrocarpon macrodidymum) as causal agent disease. Pathogenicity tests reproduced disease symptoms after six months fulfilling Koch’s postulates. D. is soilborne pathogen to be considered great economic importance P. lusitanica, especially under favorable conditions such stress and/or reduction vitality. increasingly frequent reports caused by various nurseries suggest that pot cultivation, together with prolonged drought periods, may play role favoring infections. To best our knowledge, this first report worldwide occurrence macrodidyma.