HOSTS AND NON-HOSTS IN THE DIAGNOSTIC STRATEGY OF PLANT-VIRUSES

Beside the increasingly sensitive and reliable methods available for the diagnosis and identification of the plant viruses, plants susceptible or resistant to one virus or virus group are not dispensable either. In the diagnostic strategy an essential viewpoint is to determine the common and differing characteristics of the individual viruses, in which important role is played by the knowledge of the natural and experimental host range and non-host range. In certain cases (e.g., discovery of resistance-breaking strains) a host range is more discriminating than other tests. Besides emphasizing that the role of plants in diagnostics must not be overestimated, it can be established that in the case of 232 mechanically transmissible viruses belonging to 24 virus groups, 141 hosts rendering possible the positive diagnosis of the individual viruses could be selected. The 133 selected non-hosts, on the other hand, are suitable for the exclusion or negative diagnosis of the individual viruses. Knowing the hosts and non-hosts of the various viruses we were able to select plants of which 79 enabled the positive diagnosis of the individual virus groups, while 59 plants were found to be suitable for the negative diagnosis of virus groups. We should like to emphasize that the host plants and non-hosts alone cannot provide a reliable basis for the differential diagnosis of the viruses and virus groups. For this modern virological methods are required, though these methods cannot dispense with host plant information concerning the viruses and virus groups.