INCIDENCE OF SWEET CHERRY VIRUSES IN SHANDONG PROVINCE, CHINA AND A CASE STUDY ON MULTIPLE INFECTION WITH FIVE VIRUSES

Leaves were collected from a total of 62 trees displaying virus-like disease symptoms such as rugose mosaic in leaf, irregular shaped leaf blades or small leaf blades in a survey of sweet cherry (Prunus avium L. cv Red Lamp) in Shandong Province, the largest cherry production area in China. Reverse transcription-polymerase chain reaction (RT-PCR) analysis indicated that Prunus necrotic ringspot virus (PNRSV), Prune dwarf virus (PDV), Little cherry virus-2 (LChV-2), Cherry virus A (CVA) and Cherry green ring mottle virus (CGRMV) were present and that most of the samples (70%) were infected by at least two viruses. A case study in this survey of two selected trees revealed that a mixed infection with these five viruses simultaneously caused two types of field symptoms: late-maturity in fruits or fruit blast. Real-time quantitative RT-PCR analysis revealed that the relative proportion of the virus titers was distinct in the two sampled trees. The PNRSV titer was significantly higher than the four other viruses in the trees that exhibited fruit blast. Phylogenetic analysis of the PNRSV coat protein (CP) gene showed that the isolates HSY-4-1 and X-3, obtained from the two sampled trees separately, were classified into different subgroups of Group I isolates, which is characterized by a six-nucleotide insertion. A non-synonymous substitution was identified in the six-nucleotide insertion in the PNRSV CP gene in one of the two isolates. This is the first detailed study of the incidence of multiple sweet cherry viruses in China.