|Riassunto in Inglese:|
Olive trees are infected with systemic pathogens such as viruses and phytoplasmas as well as agents of diseases of unknown etiology. The first report of a probable viral disease of olive (Olea europea) trees goes back to 1938 (Pesante, 1938). Since then, several viruses and phytoplasmas were reported in the Mediterranean Countries where olive is economically important and olive oil is considered one of the main components of the Mediterranean diet.
From the virological point of view, three different states of a pathogen infection may be recognized in olive trees: 1) diseased plants from which no causal agent has been identified; 2) symptomless plants from which various viruses have been isolated; 3) plants showing vegetative disorders, such as yellowing and leaf and fruit malformation, associated with infection by a virus or a phytoplasma.
The first experimental evidence of a true viral infection in olive trees was recorded in 1976 by chance during the observation of pollen grains of a symptomless plant of cv. ‘Corregiolo’ from Tuscany central Italy, (Pacini and Cresti, 1977). These isometric virus-like particles were identified as Strawberry latent ringspot virus (SLRSV) by Savino et al. (1979) and subsequently were associated with specific leaf symptoms in cv ‘Ascolana tenera’ (Marte et al., 1986). Subsequently, after 1980’s, a large number of viruses were identified from olive trees.
In 1996 yellowing and witches broom’s symptoms, resembling those caused by phytoplasmas in other fruit trees, were observed in orchards of north and central Italy respectively. Further investigations revealed the detection of phytoplasmas in midrib tissue of infected leaves (Poggi Pollini et al., 1996; Del Serrone et al., 1996).