First Report of Pyrus pyrifolia Cryptic Virus Infecting Pear in Korea

Abstract

Pyrus pyrifolia cryptic virus (PpCV), a new member of the genus Deltapartitivirus with three double-stranded (ds) RNA molecules (dsRNA1, 2, and 3) in the family Partitiviridae, was recently identified from pear (Pyrus pyrifolia) in Japan (Osaki et al. 2017). In 2017, one of three pear trees of cultivar Gamcheonbae in Naju, Korea, showed small leaves, stunted growth, and reduced fruit yield. Total RNA was extracted from the symptomatic plant and subjected to high-throughput sequencing; after Ribo-Zero Plant treatment, a cDNA library was prepared using an Illumina TruSeq Stranded Total RNA kit and sequenced by the Illumina HiSeq 4000 system. Analysis of the Trinity software (r20140717)-assembled sequence data with BLASTN searches against the NCBI viral genome database allowed the identification of three contigs of 1,563, 1,478, and 1,468 nt sharing 99.94, 99.93, and 100% nucleotide identities with dsRNA1, 2, and 3 of the reference PpCV isolate (GenBank AB012616, LC221824, and LC221825, respectively). Four previously described pear-infecting viruses were also detected in the sample: apple stem grooving virus, apple stem pitting virus, apricot latent virus, and apple green crinkle associated virus. To confirm the presence of PpCV, primers PpRd1/PpRdr (Osaki et al. 2017) were used for dsRNA1, and virus-specific primer pairs dsRNA2F/dsRNA2R (5′-AAAGATACGCTTGCGCAGAA-3′/5′-ATCTAGGAGCCAGCATGGTC-3′) and dsRNA3F/dsRNA3R (5′-ACCAGAATGTCTAACGACGAAGC-3′/5′-CTTGGACATCGTAGGCTCCGA-3′) were designed based on the contig sequences. Reverse transcription polymerase chain reaction (RT-PCR) products of the expected 612, 771, and 943 bp were obtained only from the symptomatic tree, cloned, and sequenced; the sequences (LC515194, LC488171, and LC488172) showed 99.84, 99.87, and 99.89% identity with the corresponding PpCV reference sequences of dsRNA1, 2, and 3 (Osaki et al. 2017), respectively. To survey the sanitary status of other pear trees, 16 samples were collected from various pear cultivars and subjected to RT-PCR detection for PpCV. Seven of these samples were positive for PpCV but did not show the same symptoms as the initial PpCV-infected Gamcheonbae tree, suggesting that those symptoms resulted from a complex mixed-virus infection. Further study is needed to understand the effect of PpCV on pear growth. To our knowledge, this is the first report of PpCV infecting pear in Korea.