Identification and characterization of Peach latent mosaic viroid and Hop stunt viroid in different peach cultivars showing dapple fruit, fruit yellow mosaic and cracked suture symptoms

M Luigi, F Faggioli, M Barba, L Giunchedi
From the early 1990s, a fruit peach syndrome characterized mainly by small discoloured spots (dapple fruit) and/or yellow areas on the skin (yellow mosaic), cracked suture and deformations was identified in most commercial orchards in the Emilia Romagna region (Northern Italy). In the past, Peach latent mosaic viroid (PLMVd) and Hop stunt viroid (HSVd) have been detected in trees with symptomatic fruits. In order to ascertain the presence and spread of these two viroids, symptomatic fruit
more » ... s were collected from five different cultivars: 'Royal Glory', 'Crimson Lady', 'Grenat', 'Diamond Princess' and 'Laura'. Dapple fruit symptoms affected all cultivars, 'Grenat' samples also showed evident yellow mosaic and fruit deformation, and 'Royal Glory' severe cracked sutures. The results showed a large diffusion of the two viroids, mainly in mixed infections. Anvaluation of the role the viroids could play in symptom expression has been complicated by the high number of samples infected by both viroids (60%). Nonetheless, 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, seems 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 could have influenced the symptom expression. Moreover, the molecular characterization of some PLMVd isolates does not show any correlation between nucleotide sequence and symptoms although new PLMVd variants were identified.