Management of European fruit tree and grapevine phytoplasma diseases through genetic resistance

In view of the great economic and social importance of fruit tree and grapevine phytoplasma diseases and the difficulties to confine these diseases, the use of resistant plant material would be of great benefit. Natural genetic resistance could be identified in the germplasm of fruit trees and grapevine, but only recently molecular work started to elucidate the mechanism of this resistance. Knowledge about the mode of action of the resistance is, however, needed to evaluate the stability of an identified resistance and the possibility that the genetically highly variable phytoplasmas might break it. The practical application of genetic resistance is most advanced in apple where promising apple proliferation-resistant rootstock genotypes have been selected and can now pass to the final step of agronomic evaluation. In grapevine the research is actually focused on different topics such as definition of a standard protocol for assessing the level of susceptibility, the phytoplasma titer in the infected plants, and thus the identification of truly tolerant and resistant varieties, and identification of the molecular traits associated with susceptibility, resistance and tolerance to grapevine yellows.