Incidence and genetic diversity of Prune dwarf virus in sweet and sour cherry in Bulgaria

Abstract

Sweet cherry is an important fruit crop in Bulgaria. One of the most common viruses of sweet cherry and other stone fruits in the world is Prune dwarf virus (PDV). Field surveys were conducted in 43 commercial and 3 collection sweet and sour cherry orchards at 10 locations in six regions of Bulgaria. Leaf samples from 2090 trees showing and not showing virus-like symptoms were tested by double antibody sandwich-enzyme linked immunosorbent assay (DAS-ELISA) for PDV infection. The average PDV infection level in sweet and sour cherry was 14.4%. In 92.4% of the trees, PDV caused single infection, whereas in 7.6%, it caused mixed infection with Prunus necrotic ringspot virus (PNRSV). Visual observations were made to connect the symptoms with PDV infection. There were PDV symptoms in 56.2% of infected trees whereas, 43.8% of the trees were asymptomatic. The coat protein (CP) sequences of 14 isolates from four regions were determined. The obtained sequences were 654 nucleotides (nts) in length, translated to 218 amino acids. Sequence comparisons showed 87%–100% to 93%–100% identity at nucleotide and amino acid level, respectively. Phylogenetic analyses using nucleotide and amino acid sequences of the CP genes of PDV isolates from Bulgaria and 38 cherry isolates retrieved from the GenBank database indicated the existence of three and two phylogenetic groups, respectively. No association between the phylogenetic grouping of the studied isolates and the symptoms of infected trees and/or the sampling-region was observed.