Molecular Characterization and Distribution of Apple Chlorotic Leaf Spot Virus on Apple in China

Abstract

Apple chlorotic leaf spot virus (ACLSV) is one of the most economically important latent viruses infecting apple in China. This is the first report of the almost complete nucleotide sequence and the characterization of the genome of a Chinese isolate (ACLSV-MS, GenBank Accession Number KC847061) from apple. Based on the genome nucleotide sequence, ACLSV-MS showed the highest identity (99.4%) to isolate ACLSV-B6 (GenBank Accession Number AB326224) from apple in Japan and the least identity (69.5%) with isolate TaTao5 (GenBank Accession Number: EU223295) from peach in the USA. The occurrence and distribution of ACLSV in China were also recorded. Three hundred and twenty-seven apple samples (40 different cultivars) collected from 56 sites in 13 provinces of China were tested by RT-PCR. The virus was detected in all regions surveyed (the provinces of Heilongjiang, Liaoning, Hebei, Beijing, Henan, Shanxi, Shaanxi, Shandong, Gansu, Ningxia, Xinjiang, Sichuan and Yunnan), with an average incidence of 69.7%. The positive samples in Heilongjiang province were highest with an incidence of 100% followed by Henan province with an incidence of 86.7%. The positive samples in Liaoning and Shanxi were the lowest with an incidence of 50%. The occurrence of virus in five common cultivars was determined. The percentage of ACLSV was highest in cv. Gala with an incidence of 33.3%, while lowest in cv. Starking with an incidence of 18.2%. It was also found in younger (≤20 years) apple orchards the occurrence of ACLSV decreased with the increase of tree age, but when trees were more than 20 years old, the occurrence of ACLSV increased. This is the first extensive survey in the last decade in China for monitoring ACLSV, which provides important information for ACLSV control in China.