A journey of discovery: a multi-stage diagnostic procedure identifies Curtobacterium flaccumfaciens pv. allii as a new potential threat to maize

In the current scenario of globalized markets and climate change, phytosanitary risks are greater than ever before: the former facilitates the spread of pests over long distances, while the latter creates environmental conditions favourable for the establishment of pests in new areas. This reinforces the need for caution and constant vigilance regarding outbreaks of new pathogens. In 2022, symptoms including chlorotic streaks, stunted growth and wilting were observed on maize plants in Northern Italy. Diagnostic procedures to identify known pathogens associated with these symptoms (such as Pantoea stewartii subsp. stewartii) produced negative results but allowed the isolation of bacterial colonies that were identified as the putative causative agent of the symptoms. Sequencing of 16S gene initially identified these colonies as Curtobacterium flaccumfaciens pv. flaccumfaciens but specific assays for this pathogen gave negative results, prompting several molecular biology and biological assays, and whole genome sequencing to identify the taxonomy of the bacterial isolates, ultimately determining them to be Curtobacterium flaccumfaciens pv. allii. Subsequent pathogenicity assays verified Koch’s postulates by inoculating the isolates on maize, observing the development of symptoms, and re-isolating the bacteria from the infected plants, confirming the status of C. flaccumfaciens pv. allii as a newly reported pathogen of maize. To date there is no information on this organism and the damage it may cause in the field. Further studies are therefore needed, to investigate its epidemiology, pathways and even possible host range, and determine how dangerous this pathogen could be to agriculture.