The host range of gentian witches' broom MLO (GWM) and its modes of transmission by the leafhopper vector, Scleroracus flavopictus, were studied. Fifty-three species of plants belonging to 20 families were infected with GWM, including Brassica campestris (Chinese cabbage), Cucumis sativus, Lycopersicon esculentum, Apium graveolens and others. MLO particles were detected in the phloems of a lot of infected plants by electron microscope, and the tests of back inoculation to healthy plants were

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... o successful by S. flavopictus. The percentage of acquisition of GWM by the individuals of S. flovopictus from diseased plants increased depending on the length of acquisition feeding periods, showing 60% for 1 day or 80% for 7 days at 28C. The percentage of the diseased plants increased in proportion to the length of inoculation feeding periods, and reached to the peak with in the periods of 12 to 24 hours. The feeding periods of S. flavopictus for transmitting GWM ranged from 18 to 30 days with average of 22 to 24 days at 28C. The leafhoppers were able to transmit GWM persistently until death and retension periods of GWM in S. flavopictus were 4 to 60 days.