Exotic Virus and Virus‐like Diseases of Fruit Trees1

Abstract

According to the results of enquiries by the ISHS Working Group on fruit‐tree virus diseases, about 40 of these could be considered as exotic for the EPPO area. In fact, most are probably due to the same pathogens and no more than 12 exotic diseases of some economic importance exist. Those which are described here are, with a few exceptions, those reported in the EPPO Al list and in the EEC directives. Some are associated with mycoplasma‐like organisms (X disease, peach rosette, peach yellows, little peach), others with rickettsia‐like bacteria (peach phony, plum leaf scald), others with viruses (peach yellow bud mosaic, prunus stem pitting, apple union necrosis, cherry rasp leaf, flat apple, plum line pattern) and some, at last, are of unknown origin (peach mosaic). Most of these diseases show a natural spread, are able to infect many different species and would find, in the EPPO area, favourable conditions to settle and spread. Avoiding introduction of exotic diseases requires that the fruit‐tree growing countries, and especially those which have recently developed their fruit‐tree industry, should complete an inventory of the viruses present. ISHS has been struggling over recent years to standardize indexing methods and to arrive at better and more uniform international virus testing. The tremendous progress recently observed in the field of indexing now allows a contamination to be detected within weeks or even hours and consequently should help avoid or limit the introduction of new pathogens.