| Abstract: | Although the causal agents of several important fruit-tree diseases have been identified, the aetiology of many remains unknown. Some prevalent viruses seem to have little effect on certain rootstock/cultivar combinations, while others reduce fruit yields and a few can make orchards quite worthless. Most EEC countries have 2 certification schemes; one requires only that plants are true-to-type and free from visible virus diseases, while to be eligible for the other scheme the plants must be propagated from virus-tested scionwood trees and rootstocks. The use of virus-free clones has resulted in better bud-take, more even growth in the nursery and trees that will often be more productive in the orchard. Diseases, such as sharks (plum pox), that have insect vectors will be difficult to control in nurseries if the virus occurs in nearby plants. |
