Development and validation of a UHPLC-ESI-QTOF mass spectrometry method to analyze opines, plant biomarkers of crown gall or hairy root diseases

•Opines are biomarkers specifically produced by agrobacteria-infected plants.•A general, specific and sensitive UHPLC-ESI-MS QTOF method for opines was developed.•Detection selectivity of opines was validated in pure solution and plant extracts.•A powerful tool with easy sample preparation for crown gall/hairy roots diagnosis.•Nopaline, octopine and mannopine were accurately quantified in plant extracts.