Observations of <i>Botrytis cinerea</i> damage on oleander: First identification of the pathogen by classical and molecular methods in Hungary

Oleander (<i>Nerium oleander</i> L.) is a popular ornamental plant in Hungary and is known to be the host of many pathogens, only some of which have been studied so far. Although oleander is threatened by many fungal pathogens, only a few cause significant problems, such as <i>Ascochyta oleander</i> (Sacc et Speg) or <i>Verticillium dahliae</i> (Kleb). In 2019 and 2022, small leaf spots and brownish necrotic spots were observed on oleander leaves and branches in some plant nurseries in Hungary. Usually, these symptoms are associated with a fungal disease, but he pathogen causing this disease has not been investigated in Hungary, so the aim of the study was to identify the pathogen. Pathogen from the infected plant parts was isolated onto potato dextrose agar. The colonies were grey with aerial mycelium and produced black-colored sclerotia aer four weeks. The conidia were unicellular, hyaline to slightly brown, and elliptical, with an average size of 6.18 × 5.9 μm. Following Koch’s postulates, all isolates were pathogenic. Based on the morphological characteristics of the pathogen, all six isolates were identified as <i>Botrytis cinerea</i> (Pres), which was confirmed by the nucleotide sequence analysis of PCR products by amplifying the 18S-28S rRNA region. Although symptoms caused by the pathogen on oleander flowers have been widely reported, this is the first classical and molecular identification study of <i>Botrytis cinerea</i> causing symptoms on the stem of oleander in Hungary.