Occurrence pattern of viral infection on Pear in Korea and genetic characterization of apple scar skin viroid isolates

Apple chlorotic leaf spot virus (ACLSV), apple stem pitting virus (ASPV), apple stem grooving virus (ASGV), and apple scar skin viroid (ASSVd) are economically important viruses infecting pear trees worldwide. A large-scale survey was carried out in five major pear producing area sof Korea in 2017 and 2018 to investigate the occurrence patterns of these viruses in pear leaves and fruit. The virus incidence rate was 13.8% for ACLSV, 31.7% for ASPV, 95.3% for ASGV, and 3.6% for ASSVd. Fruit samples were 2.8% for ACLSV, 28.4% for ASPV, 99.0% for ASGV, and 13.8% for ASSVd. The most common type of mixed infection was ASGV+ASPV (22%). Furthermore, the ASSVd genome was completely sequenced and showed 99% sequence identity at a nucleotide level to other isolates.