Evaluation of the phytosanitary status of the Prunus species in the National Clonal Germplasm Repository in California: survey of viruses and viroids.
The USDA National Clonal Germplasm Repository (NGCR) at the University of California, Davis is recognized as one of the richest sources of Prunus species material in the US. The repository maintains more than 2450 trees representing 96 taxa collected from around the world. However, the phytosanitary status of the NCGR Prunus collection has not been thoroughly evaluated. In this study, a comprehensive screening of a selected subset of the collection for virus and virus-like diseases affecting Prunus trees has been completed. Two factors were considered for selecting the trees: the country of origin and the observation of suspicious disease symptoms. A total of 221 trees representing 185 different cultivars of cherry, almond, peach, apricot and plum were sampled. Conventional RT-PCR detection was used to test for 13 different viruses and two viroids. The pathogens included in the survey were Prunus necrotic ringspot virus (PNRSV), Prune dwarf virus (PDV), Plum bark necrosis stem pitting-associated virus (PBNSPaV), American plum line pattern virus (APLPV), Cherry virus A (CVA), Cherry leafroll virus (CLRV), Cherry rasp leaf virus (CRLV), Cherry green ring mottle virus (CGRMV), Cherry necrotic rusty mottle virus (CNRMV), Apple chlorotic leafspot virus (ACLSV) Tomato ringspot virus (ToRSV), Little cherry virus 1 (LChV-1), Little cherry virus 2 (LChV-2), Peach latent mosaic viroid (PLMVd) and Hop stunt viroid (HSVd). Though the majority of these trees were asymptomatic, all tested pathogens were detected except for ToRSV and CRLV. Two of the viruses detected (ACLSV and LChV-2) had never been reported from California. Incidence of PNRSV in tested trees was the highest (55 trees) followed by the two viroids (PLMVd and HSVd), with 33 and 32 infected trees, respectively. The incidence for the rest of the pathogens ranged between 0 to 19 trees. The infection rate of all tested samples ranged from 0.5% to 24.9%.