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First Report of Sweet potato leaf curl Georgia virus on Sweet Potato in China

Begomoviruses infecting sweet potato (Ipomoea batatas) are phylogenetically distinct from other members of the genus Begomovirus, and have been named “sweepoviruses” (1). Sweepoviruses cause sweet potato yield losses and cultivar decline, and have been found in China (1,3). In 2011, a survey was conducted to determine the incidence, genetic diversity, and distribution of sweepoviruses in China. Thirty sweet potato cuttings showing upward leaf curl, leaf roll, chlorosis, and stunting were collected from fields in Jiangsu, Guangxi, Guizhou, Shanxi, Henan, and Hebei Provinces. Five-leaf growth stage I. setosa plants were inoculated by side-grafting with scions from these samples, and grown in an insect-proof greenhouse in 20-cm-diameter clay pots. Each sample was grafted onto three replicate plants. Healthy, non-grafted I. setosa plants were used as the negative control treatment. Total nucleic acids were extracted from 100 mg fresh leaves harvested 30 days post-inoculation (dpi) from symptomatic and negative control plants using the Universal Genomic DNA Extraction Kit (TaKaRa, Dalian, China). Universal primers for amplification of Geminiviruses (BM-V [5′-KSGGGTCGACGTCATCAATGACGTTRTAC-3′] and BM-C [5′-AARGAATTCATKGGGGCCCARARRGACTGGC-3′]) (2) were used to amplify the begomovirus A component by PCR assay. A DNA fragment of the expected size (2.8 kb) was obtained from grafted leaf samples of the Hebei Province plant, and was cloned into the pMD-19T vector (TaKaRa). The recombinant plasmid was transformed into competent cells of Escherichia coli strain JM109, and the inserted fragment sequenced. The nucleotide sequence obtained (GenBank Accession No. JX448368) was 2,785 nt long, and contained two open reading frames (ORFs) in the virion sense, and four ORFs in the complementary sense, similar to other monopartite begomoviruses (1). The sequence was compared with sequences in GenBank using BLAST. The results revealed the greatest nucleotide sequence identity, 90.8%, with that of the Sweet potato leaf curl Georgia virus (SPLCGV) from Georgia, United States (AF326775). The sequence also shared identities of <89% with other sweepoviruses, and was therefore designated SPLCGV-China: Hebei: 2011. Comparison of the complete genome sequence of SPLCGV-China: Hebei: 2011 with SPLCGV revealed an 18 nucleotide insertion between AV-1 and AC-3. The results confirmed that the sweet potato sample from which SPLCGV-China: Hebei: 2011 was obtained was infected with SPLCGV. To our knowledge, this is the first report of the natural occurrence of SPLCGV in China. This study will assist with understanding the presence of this virus and genetic diversity of sweepoviruses in China.

References: (1) H. P. Bi and P. Zhang. Arch. Virol. 157:441, 2012. (2) R. W. Briddon and P. G. Markham. Mol. Biotechnol. 1:202, 1994. (3) Y. S. Luan et al. Virus Genes 35:379, 2007.