First report of Curtobacterium allii in Italy and in the EPPO region
Curtobacterium allii is a new bacterial species which was first described in 2023 from diseased onion bulbs (Allium cepa) in Texas (USA).
In Italy, samples of maize (Zea mays) grown in the province of Cremona (Lombardia region) were submitted to the Plant Protection Service laboratory by a private company in May 2022 for diagnosis. Maize samples showed symptoms including longitudinal streaking on leaves, yellowing and discoloration. In addition, maize plants showed reduced vegetative growth and in some cases leaf desiccation. These affected maize plants were grown in a demonstration field and were destroyed after the sampling, thus preventing any further official investigations.
Specific molecular tests were carried out to exclude the presence of the quarantine pathogens Curtobacterium flaccumfaciens pv. flaccumfaciens (EPPO A2 List) and Pantoea stewartii subsp. stewartii (EPPO A2 List). DNA from the isolated colonies was amplified using general 16S primers and the amplicons were sequenced. In addition, individual colonies were sequenced using an Illumina platform and identified as the new species Curtobacterium allii sp. nov. The isolated C. allii colonies were inoculated onto onion bulbs and showed to cause rot as reported in the initial description by Khanal et al. (2023). In addition, Koch's postulates for this pathogen were demonstrated, showing that after infection conducted under controlled conditions, maize plants showed the same symptoms as those observed in the field in Cremona. This is the first detection of the bacterium on the territory of the European Union. No phytosanitary measures could be imposed because the crop in the demonstration field had already been destroyed. Since this report, there have been no further symptoms observed in the field nor any positive test results.
Sources
NPPO of Italy (2024-05).
Khanal M, Bhatta BP, Timilsina S, Ghimire S, Cochran K, Malla S (2023) Curtobacterium allii sp. nov., the actinobacterial pathogen causing onion bulb rot. Antonie Van Leeuwenhoek 116(2), 83-96.