OCCURRENCE OF PLUM POX VIRUS IN CHERRY ORCHARDS IN UKRAINE
Pavliuk L, Udovychenko K, Riaba I.
Institute of Horticulture of the National Academy of Agrarian Sciences of Ukraine
Plum pox virus (PPV) is a member of the genus Potyvirus in the Potyviridae family. In general, PPV is considered to be one of the most destructive pathogens of Prunus species, yield losses can reach 30-40%, and in some years on sensitive varieties – 70-90%. The following PPV strains are known today: M, D, ЕА, C, Rec, W, Т, CR, An, and CV. Recently new PPV strains have been reported in neighboring countries, infecting sour and sweet cherries, including PPV-CR and PPV-CV strains. Therefore the aim of the study was to investigate distribution of PPV in cherry orchards and to determine strains of isolates.
During the vegetation period of 2018-2020, 291 samples were tested, including 138 – of sweet cherry, 99 – of sour cherry, 54 – of clonal rootstocks. Samples were collected from 10 regions of Ukraine (Ivano-Frankivsk, Kyiv, Zaporizhzhya, Ternopil, Donetsk, Kharkiv, Kherson, Transcarpathian, Dnipropetrovsk, Cherkasy regions). Testing was performed by ELISA method using Loewe Biochemica GmbH (Germany) commercial test kits. ELISA was performed according to standard methods of M. Clark and A. Adams (1977). Then positive PPV samples were further tested by RT-PCR method to confirm the presence of the virus in the plant. Isolation was performed using a commercial RNeasy Plant Mini kit (Qiagen, UK) according to the manufacturer’s instructions. Commercial Verso 1-Step RT-PCR Kit ReddyMix (Thermo Scientific, USA) was used according to the manufacturer’s recommendations to set up the reaction. The following primers were used for molecular identification – P1: 5’–ACC GAG ACC ACT ACA CTC CC–3’ and P2: 5’–CAG ACT ACA GCC TCG CCA GA–3’, proposed by Wetzel et al. (1991) with expected fragment size 243 bp. The resulting amplicons were sequenced. Nucleotide sequences were compared with those deposited in the Genbank (www.ncbi.nlm.nih.gov) using BLAST 2.10.0 software.
Serological testing of the material of sour cherry, sweet cherry, and rootstocks showed that the infection of sour cherry was 7% (±0.05), while sweet cherry and rootstocks were infected only by 1.4% (±0.02) and 1.9% (±0,04), respectively. According to the results of comparison of our isolates with known ones, its affiliation to D strain was established. It should be noted that this strain is the most common in Ukraine, it includes about 83% of Ukrainian PPV isolates deposited in the Genbank. The other 17% of isolates belong to strains W, M, and Rec. The host plants are mainly peach, apricot, and plum. Characterized in this study isolates are the first PPV isolates of D strain isolated from Prunus mahaleb L. in Ukraine. Mahaleb 1 and Mahaleb 2 isolates showed 100% level of identity between themselves. When comparing all Ukrainian isolates, variability within the group was found, identity ranged between 89.5–100%, and the overall mean identity was 97%.
Since PPV isolates identified by us belong to D strain, it is necessary to further determine its ability to be transmitted to plants that are more susceptible to the virus, as well as to investigate its harmfulness in sour and sweet cherry orchards.