Multiplication of the agent of X-disease in a non-vector leafhopper Macrostelesfascifrons

The relative titre of the causal agent of X-disease of stone fruits in the non-vector leafhopper Macrosteles fascifrons was tested by injecting dilutions of M. fascifrons extracts into non-infective Colladonus montanus leafhopper vectors. The recipient C. montanus were fed on celery test plants which were then observed for X-disease symptoms. M. fascifrons were assayed at various intervals for up to 37 days after they were fed on X-diseased celery or injected with infectious extracts of the X-agent. Infectivity was detected in M. fascifrons only after 25 or 37 days in separate trials. Whole body extracts but not extracts from detached heads of M. fascifrons that had fed on X-diseased celery were infectious, whereas extracts prepared from the heads of M. fascifrons previously injected with X-agent extracts were infectious. This infectivity was retained for up to four serial passages in M. fascifrons. Electron microscopy of M. fascifrons that had been injected with extracts of the X-disease agent revealed mycoplasma-like organisms (MLO) only intercellularly and appressed to various organs in the haemocoele. No MLO were observed in uninjected M. fascifrons or those injected with extracts from non-infectious C. montanus. These results suggest that, despite multiplication of the X-agent in vivo. barriers in the gut and salivary glands prevent its transmission to plants by M. fascifrons.