|Riassunto in Inglese:|
From the early 1990s, a fruit peach syndrome characterized mainly by small discoloured spots (dapple fruit) and/or yellow areas on skin (yellow mosaic), cracked suture and deformations occurs in most commercial orchards in the Emilia Romagna region (central-north part of Italy). In the past, Peach latent mosaic viroid (PLMVd) and occasionally Hop stunt viroid (HSVd) have been detected in trees with symptomatic fruits. In order to ascertain the presence and the frequency of these two viroids, fruit samples have been collected from five different cultivars: ‘Royal Glory’, ‘Crimson Lady’, ‘Grenat’, ‘Diamond Princess’ and ‘Laura’. Dapple fruit symptoms affected all cultivars, whereas ‘Grenat’ samples also showed evident yellow mosaic and fruit deformation and ‘Royal Glory’ severe cracked sutures. The results obtained showed a large diffusion of the two viroids, mainly in mixed infection; more specifically PLMVd was found in 100% of ‘Royal Glory’, ‘Diamond Princess’ and ‘Laura’ samples, in 90% of ‘Grenat’ samples and in 70% of ‘Crimson Lady’ samples; HSVd affected 100% of ‘Crimson Lady’ and ‘Laura’ samples, 90% of ‘Royal Glory’ samples and 30% of ‘Grenat’ samples, whereas it was not found in the ‘Diamond Princess’ samples. The role that the viroids could play in the expression of the symptoms in the fruit peach samples has been complicated by the high number of samples infected by both viroids (60%); in any case, PLMVd was confirmed to be strictly associated with the yellow mosaic, cracked suture and fruit deformation symptoms. The aetiological origin of the dapple fruit disease, however, seem to be more complicated, since in the ‘Diamond Princess’ only PLMVd has been found to be associated with the symptoms, whereas in all other cultivars the presence of HSVd in high percentages could have influenced the symptoms expression.