|Riassunto in Inglese:|
Temperate fruit trees are affected by many viruses, viroids and phytoplasmas which may cause considerable economical losses in their production (Németh, 1986, Fridlund 1989, Barba, 1998; Hadidi et al., 1998, 2003; Desvignes, 1999; Barba et al., 2003). These pathogens are of major concern to worldwide phytosanitary agencies as no effective cure exists to remedy the orchard trees from their infected pathogens (Matthews, 1991).
Fruit tree pathogens are transmitted by several ways which allows their survival from generation to generation through vegetative propagation of infected germplasm. In order to prevent or reduce pathogen damage, it may be necessary to produce and use pathogen-free planting material.
To design an efficient strategy for pathogen control, it is crucial to differentiate viruses, viroids and phytoplasmas according to their physical properties, i.e. their sensitivity to heat, stability in plant sap and distribution in plant tissue.
Different hypotheses of possible mechanisms involved in pathogen elimination have been proposed. The main conclusion to be drawn from different experimental approaches, however, is that pathogen elimination is an extremely pathogen/host dependent process and that no generalizations should be made.
Pathogen elimination can be achieved by different techniques such as: 1) thermotheraphy, which is performed either in vivo or in vitro, 2) meristem tissue culture, 3) a combination of in vitro thermotherapy and meristem tissue culture, 4) in vitro micrografting and 5) in vitro chemotherapy.