Molecular characterization and pathogenicity analysis of prunus necrotic ringspot virus isolates from China rose (Rosa chinensis Jacq.)

Prunus necrotic ringspot virus (PNRSV) is a viral pathogen with worldwide distribution, infecting many commercial fruit trees and ornamental plants. So far, the correlation between PNRSV infection and China rose mosaic disease has not been studied. Rose mosaic disease is characterized by severe symptoms, including mosaic, line pattern, and ringspot. Six viruses that were potentially associated with mosaic disease, including PNRSV, were tested in China roses. Only PNRSV was detected in China roses showing mosaic disease, and asymptomatic samples tested negative for this virus. This result was confirmed by small RNA sequencing, but rose leaf rosette-associated virus and rose spring dwarf-associated virus were also identified in both samples with mosaic disease and asymptomatic samples. This implied that PNRSV might be associated with China rose mosaic disease. Full genome sequences of two PNRSV isolates were determined, and the RNA1, 2 and 3 segments were found to be 3,332, 2,594 and 1,951 nucleotides (nt) in length, respectively. The three RNA segments shared 88.7-89.1% nt sequence identity in the 3'UTR, while RNA2 and RNA3 shared 98.2-99.4% identity. The higher variability in RNA1 suggests that it might have been under greater selection pressure. Phylogenetic analysis showed that the two PNRSV isolates clustered in group PV-32. Full-length infectious cDNA clones of PNRSV from China rose were constructed and used to agroinfiltrate cucumber seedlings. The inoculated cucumber leaves showed yellowing, chlorotic spots, necrosis, dwarfing, and decline at 23 to 39 days post-inoculation, demonstrating the virulence of the PNRSV isolate from China rose. These data lay a foundation for determining the molecular mechanism of rose mosaic disease caused by PNRSV.