Molecular variability of the coat protein gene of prunus necrotic ringspot virus on sweet and sour cherry in Bulgaria

Prunus necrotic ringspot virus (PNRSV) is a stone fruit tree pathogen. Field surveys were conducted in the spring of 2018 and 2019 in 58 commercial and four collection sweet and sour cherry orchards in six regions of Bulgaria. Leaf samples from 3214 trees showing and not showing virus-like symptoms were tested by enzyme linked immunosorbent assay (ELISA) for PNRSV infection. The average infection level of 5.1% was higher in sour cherry (15.5%), than in sweet cherry trees (1.8%). The coat protein (CP) sequences of 25 isolates were determined. The obtained sequences were 596 or 675-681 nucleotides (nts) in length, translated to 198 or 225-227 amino acids (aa), respectively. Sequence comparisons showed 94-100% nucleotide and 90-100% amino acid identities among the 25 isolates. Phylogenetic analysis using nucleotide and amino acid sequences of Bulgarian isolates and cherry isolates retrieved from the GenBank database confirmed clustering into the previously reported PV96-II, PV32-I, PE5-III and CH30 phylogroups. Twenty Bulgarian isolates belonged to PV96-II and five isolates to PV32-I phylogroup. No correlation was noted between PV96-II phylogrouping and the sampling region/and or symptoms of infected trees of studied isolates, while a connection to a certain degree with geographical origin of the isolates in PV32-I phylogroup, but not with the symptomatology was observed.