Nerium oleander L is a long-lasting flowering vegetatively propagated ornamental plant of the Mediterranean region, where it is a major imported flowering pot plant. Only a few bacteria can infect it such as Pseudomonas savastanoi pv. nerii, Agrobacterium tumefaciens and Xylella fastidiosa. Between 2018 and 2022 we collected several infected plant parts in our country. In 2020 we observed atypical symptoms on the leaves and stems, which were not clearly similar to the known bacterial infection of oleander. In our work, we aimed to identify the pathogen. The isolates formed yellowcoloured bacterial colonies on King-B and on YDC agar, were Gram-negative, oxidase negative and induced hypersensitive reaction on tobacco leaves. The biochemical properties were determined by API 20E and API 50CH tests. Brown necrosis was observed on oleander leaves in a pathogenicity test. Multilocus sequence analysis was used for molecular identification of the pathogen. Three housekeeping genes (gyrB, fyuA and rpoD) were amplified. According to symptoms, colony morphology, biochemical features, pathogenicity and molecular methods, the pathogen was identified as Xanthomonas arboricola. This is the first report of the plant pathogenic Xanthomonas spp. on oleander.

In Hungary, from the beginning of the 19th century, horse‐chestnut trees have been planted widely and are popular ornamental trees in public parks, along streets, and in gardens. In the summer of 2015, longitudinal cracks on the trunk and branches and the intensive oozing of brown liquid were observed from a wound in a horse‐chestnut tree in a park in Budapest. Some years later, in 2018 and 2019, the same symptoms were found in trees in other locations in Budapest. Several bacteria were reported that induce similar symptoms, including cracks and cankers on the bark of trunks and branches and sticky, white, red, brown, or black oozing. These pathogens belong to the genera Brenneria and Lonsdalea. Bark and exudate samples were taken with the aim of identifying the causal agent by conventional and molecular methods. Our results confirmed that the bacteria isolated from Aesculus hippocastanum trees belong to the genus Brenneria and phylogenetic analysis of the 16S rRNA gene region proved to have the closest phylogenetic relation with the Brenneria nigrifluens strains.

Oleander (Nerium oleander L.) is a popular woody ornamental plant, often used for decorating public areas, terraces and gardens. Many diseases may decrease in the ornamental value of these plantings. Between 2018 and 2020, plant pathogenic bacteria of oleander were examined, and many samples of infected plants were collected from different sites in Hungary. Two non-pigmented Serratia marcescens isolates were identified from oleander by classical and molecular methods. The isolates caused necrotic lesions on oleander leaves. Serratia marcescens is known as an opportunistic mammal or plant pathogen, but non-pathogenic strains are known to be useful biological control agents or plant growth-promoting bacteria. This is the first report of the plant pathogen S. marcescens from oleander, and the first identification of the bacterium in Hungary.