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First Report of Actinidia Virus 1 Infecting Actinidia chinensis in China

Peng, Q. D., Lv, R., Ning, J. C., Yang, T., Lin, H. H., Xi, D. H., Zhuang, Q. G.
Plant disease 2019 v.103 no.4 pp. 782
Actinidia chinensis, Closteroviridae, RNA, abnormal development, amino acid sequences, biotechnology, chlorosis, climate, clones, coat proteins, electron microscopy, genes, genetic variation, horticultural crops, kiwifruit, leaves, mixed infection, nucleotide sequences, particle size, plant diseases and disorders, plant viruses, planting, polymerase chain reaction, sequence alignment, staining, surveys, vines, viruses, China, Italy, New Zealand
China is the origin of Actinidia spp. (kiwifruit) and has largest kiwifruit production around the world. Although kiwifruit was domesticated only in the 20th century, it has become an important horticultural crop. A total of 17 viruses have been found in kiwifruit growing areas including China, Italy, and New Zealand since 2002 (Blouin et al. 2013, 2018; Veerakone et al. 2018). Sichuan Province has a unique geographical condition and climate for growing kiwifruit. It is the second largest area after Shanxi Province for commercial production of kiwifruit in China. With an increasing number of years of kiwifruit cultivation, suspect viral symptoms such as leaf mottle, chlorosis, and malformation are increasing. To confirm which viruses are infecting Actinidia spp. and to determine the extent of their distribution in Sichuan Province, a survey was conducted from April 2016 to May 2018. Fifty-six kiwifruit samples that showed virus-like symptoms such as feathery mottle, chlorotic and necrotic spots, and yellowing on leaves were collected from five different varieties of Actinidia chinensis at seven different geographic locations in Sichuan Province. Electron microscopy examination by negative staining for crude extracts of the symptomatic leaves revealed flexuous filaments of 9 to 10 nm × 1,350 to 1,400 nm. The particle size suggested a species of Closteroviridae. To identify the virus, total RNA of the respective samples was extracted with the EASYspin RNA Plant Mini Kit (Aidlab Biotechnologies Co., China) and reverse transcribed using random hexamers (Fermentas, Thermo Scientific). Actinidia virus 1 (AcV-1) coat protein specific primers, AcV1-CP F (5′- CGCGGATCCATGACTACCAAAGAAACGAA-3′) and AcV1-CP R (5′- ACGCGTCGACTCAATGATAACCTGAAGTGA-3′), were used to examine the presence of AcV-1, a new Closteroviridae virus recently identified in kiwi vines in Italy (Blouin et al. 2018). The results showed that 22 of the 56 kiwifruit samples generated bands of the expected size (732 bp) for AcV-1. One polymerase chain reaction amplicon from one sample from each of the seven different geographic locations was cloned into a pEASY-Blunt Zero vector (TransGen Biotech, China) and Sanger sequenced by Chengdu Tsingke BioTech Co. DNAMAN sequence alignment showed that across the seven clones, there were five different sequences, which shared 87.4 to 99.7% nucleotide sequence identity and 92.6 to 100% amino acid sequence identity (GenBank accession nos. MH557852 to MH557856). The variations were mainly concentrated in the middle domains of the coat protein genes. Further analysis showed that the five AcV-1 isolates shared 89.8 to 90.2% nucleotide sequence identity and 94.7 to 95.9% amino acid sequence identity to the corresponding gene of AcV-1 isolate K75 from Italy (KX857665, Blouin et al. 2018). Our results confirmed the widespread presence of AcV-1 in all kiwifruit planting areas that were investigated and in different varieties of A. chinensis (Hongyang, Donghong, Honghua, Jinguo, and Jinyan). Our sequence data also showed that there was genetic variability among different AcV-1 isolates in Sichuan Province. However, the role of AcV-1 as the causal agent for the symptoms observed in Actinidia is unknown, because plants were coinfected with other Actinidia-infecting viruses. To our knowledge, this is the first report of AcV-1 infecting A. chinensis in China. The apparent expansion of this virus is worthy of further attention.