First Report on the Occurrence of Tomato Yellow Leaf Curl Virus in Tennessee

In the summer of 2021, a field survey of several tomato-growing counties in Tennessee (TN) was conducted for plants exhibiting virus-like symptoms. While scouting in September in Grainger County, one of the largest areas under tomato (Solanum lycopersicum) production in TN, leaves from six tomato plants (cv. BHN 589) growing on a farm located near Rutledge were collected and subsequently stored at -80˚C. Only one of the plants exhibited symptoms typical of tomato yellow leaf curl virus (TYLCV) infection, which included chlorosis, leaf curling, downward cupping, thickening, and mottling. Total DNA was isolated using the DNeasy Plant Mini Kit (Qiagen, Santa Clara, CA) and subjected to PCR using primers TYv2337F (5'-ACGTAGGTCTTGACATCTGTTGAGCTC-3') and TYc138-R: (5'-AAGTGGGTCCCACAATTGCAAGAC-3') and Ex-Taq polymerase (Takara Bio, Mountain View, CA) to amplify a 634-bp genomic fragment of TYLCV (Alkowni et al. 2019). Primers against tomato elongation factor-1 served as internal PCR control (Dias et al. 2023). Each primer set amplified amplicons of expected sizes; however, the TYLCV fragment was detected only from the plant exhibiting typical symptoms of infection. Amplicons were purified with the QIAquick PCR purification kit (Qiagen) and sequenced directly bi-directionally by Eurofins USA using the above primers. The resultant sequences were edited and analyzed with CLC Genomic Workbench v. 24.0.1. Blast analysis of the sequences (606 nts) against those available in GenBank showed 93 TYLCV isolates with over 95% nucleotide sequence identity. Subsequently, the full-length genome was PCR amplified using primers TYBamHIv (5'- GGATCCACTTCTAAATGAATTTCCTG-3') and TYBamHI2c (5'-GGATCCCACATAGTGCAAGACAAAC-3') (Rojas et al. 2007), ligated into pGEM-T (Promega, Madison, WI) and cloned. Plasmids were purified using QIAprep Spin Miniprep kit (Qiagen) and five independent plasmids clones were sequenced using Oxford Nanopore sequencing (v14 library chemistry & R10.4.1 flow cell) by Eurofins USA. The resultant sequences were edited and analyzed with CLC Genomic Workbench and a consensus sequence representing the full-length genome (2,781 nts) was generated and submitted to GenBank (Accession No. PP505780). Blast analysis showed over 98% nucleotide sequence identity with 100 TYLCV isolates from GenBank. The highest sequence identity of 98.6% was with the sequence of an isolate from Florida (AY530931). To the best of our knowledge, this is the first report of the occurrence of TYLCV in TN. The virus was detected in a tomato plant grown from seed. The seed transmissibility of TYLCV remains controversial (Perry 2018; and references therein); thus, the most likely source of infection in this report is transmission by rare viruliferous vectors (Bemisia tabaci). It remains unknown, however, whether TYLCV is endemic in TN, or recently introduced by mobile vectors from neighboring states. The presence of TYLCV has been reported in Alabama (Akad et al. 2007), Kentucky (de Sá et al. 2008), Mississippi (Ingram and Henn 2001), Georgia (Momol et al. 1999) and North Carolina (Polston et al. 2002). The B. tabaci vector of the virus has sporadic occurrences in crops within TN (Li et al. 2021). Tennessee is one of the leading tomato producers exporting globally with production covering over 1,300 hectares and over 430 producers (Dias et al. 2023). Because of the potential threat of TYLCV to tomato industry in the state, additional surveillance measures need to be put in place to determine TYLCV incidence.