|Riassunto in Inglese:|
Hop stunt viroid (HSVd) has been found in a wide range of hosts where the infection appears to be latent, whereas in others (hop, cucumber, citrus, Japanese plum, peach) it is frequently pathogenic. In this work, the presence of HSVd has been found to be associated to symptoms of dapple fruit and occasionally fruit rugosity in plum seedlings 4 years old obtained from cross breeding. In particular, the plum samples have been analyzed for the presence of viroids (HSVd and PLMVd) and viruses (PPV, ACLSV, ApLV, PDV, PNRSV, ApMV). HSVd was found in all symptomatic samples, whereas no other viruses or viroids were found in the analyzed samples with the exception of ACLSV, rarely and sporadically detected. All the HSVd isolates have been cloned and sequenced and a high percentage of homology (98-100% with the exception of one clone obtained from the isolate F20) has been obtained among them, making it possible to hypothesize a potential unique origin of the infection. For this purpose, the ‘Black Sunrise’ and ‘Black Glow’ plum trees, the cultivars used in the breeding as pollen donors, have been analyzed. The results showed the presence of HSVd in parental plants and the obtained sequences resulted similar (95-100 %) to the isolates found in the seedlings, suggesting a possible role of the breeding in the dissemination of the viroid. In the next months, pollen from infected parental plants will be collect and analyzed to confirm the possible presence of HSVd. Moreover, these results confirm the hypothesis that HSVd could be the cause of the dapple fruit and fruit rugosity diseases.