The occurrence of viruses and viroids in ornamental citrus mother plants in Tuscany (Central Italy)

Citrus tristeza closterovirus (CTV) has been found several times in the last decades in Italy, and plant protection services are involved in monitoring and surveillance. Although orchards linked to the citrus industry are well monitored, there is an underestimated risk of viruses or virus-like diseases in ornamental nurseries. Our aim was to modify a CTV monitoring program to include other viruses (Citrus variegation virus, CVV; Citrus psorosis virus, CPsV) and viroids (Citrus exocortis viroid, CEVd; Hop stunt viroid, HSVd; Citrus bent leaf viroid, CBLVd; Citrus dwarfing viroid, CDVd; Citrus bark cracking viroid, CBCVd). Ornamental mother plants were monitored for four years in 15 nurseries in two locations in central Italy using inexpensive multiplex RT-PCR protocols. CTV incidence was 1.6-13.5%, with an average distribution of 11.9%. The average incidence of CVV and CPsV was 6.3% and 2.7%, respectively. Higher CTV, CVV and CPsV incidences were observed in C. x paradisi, C. grandis and C. x clementina. The most widespread viroid identified was CEVd (32.9%), frequently observed in C. x limonia and C. limon. HSVd (10.5%), and CDVd (7.1%) were mostly found in C. x limonia. Lower infection rates were observed for CBLVd (2.0%) and CBCVd (1.4%). However, the nurseries' response to the virus alert by the protection services was only partially effective. Although the CTV incidence was lower in nurseries re-checked after the initial detection, it was not eradicated from two nurseries out of three, and the occurrence of viroids was reduced in just one nursery. Given that dangerous viruses along with the concomitant spread of viroids have unfortunately become a fact of every day life, multiplex RT-PCR diagnoses are likely to play an increasing role in warning nursery managers of possible infections.