First Report of Plum Pox Virus on Plum in Uzbekistan

Abstract

Apricot, sweet cherry, plum, and peach are economically important stone fruit crops in Uzbekistan. Plum pox virus from the genus Potyvirus in the family Potyviridae is the causal agent of sharka disease. Plum pox virus (PPV) is the most destructive viral pathogen of stone fruit trees. No information is available on PPV occurrence in Uzbekistan. In 2019, plum (Prunus domestica) trees exhibiting foliar pale green rings and spots were observed in a 21-year-old orchard of the local cultivar ‘Ispanskiy’ in the Tashkent region of Uzbekistan. One symptomatic leaf was taken from each of four trees growing at the corners of this orchard. The samples were tested for PPV by double antibody sandwich ELISA using reagent set SRA 31505/0500 (Agdia, U.S.A.) and immunocapture RT-PCR using the coating antibody CAB 31505/0500 (Agdia) and PPV-specific P1/P2 primers (Wetzel et al. 1992). PPV was readily detected in each sample by both methods. PCR products of the expected size (198 bp) were generated by RT-PCR using P1/PD strain-specific primers (Olmos et al. 1997), indicating that the isolates belonged to the strain D. No positive reaction was observed with primers specific to the PPV strains M, W, and C, indicating no mixed infection. All four isolates were recognized by triple antibody sandwich ELISA using PPV-D-specific antibody 4DG5 (K-12B kit, Agritest, Italy), thus confirming the results of the strain-specific RT-PCR. The 3′-terminal genomic sequences encompassing the coat protein (CP) gene and flanking sequences of the NIb gene and 3′-noncoding region were amplified using NIbF/4CPR1 primers (Chirkov et al. 2016), and the PCR products of about 1.3 kb were sequenced using the Sanger method. The sequence of isolates Uz2 and Uz4 was identical, and isolates Uz1, Uz2, and Uz3 shared 99.1 to 99.6% and 99.0 to 99.3% identity at the nucleotide and amino acid levels, respectively. The low genetic diversity of Uzbek isolates suggests their common origin. The ¹¹DAG¹³ motif responsible for aphid transmission, the PPV-D-specific ⁵⁵QPATKP⁶⁰ epitope, and the universal ⁹⁴DRDV(I)DAG¹⁰⁰ epitope (Candresse et al. 2011) were found in the deduced N-terminal sequence of the CP of all the isolates. The 3′-terminal genomic sequences of the Uz1, Uz2, and Uz3 isolates were deposited in GenBank under accession numbers MT038048 to MT038050. Phylogenetic analysis of the CP gene assigned Uz1, Uz2, and Uz3 to the cluster of PPV strain D isolates (LT600779 to LT600782) detected in a Prunus germplasm collection from neighboring Kazakhstan (James et al. 2017) and the isolate BIII/2 (GU461890) from Slovakia. According to BLASTn, the Uzbek isolates were most closely related to the Kazakh isolate P7R1 from plum (LT600780) (99.2 to 99.5% nucleotide identity). To the best of our knowledge, this is the first report of PPV from Uzbekistan. This finding expands the geographical distribution of the virus and encourages further studies on PPV prevalence, host range, and genetic variability to reduce its impact on the fruit-growing industry.