First Report of Bidens Mottle Virus Causing Mild mottle and Leaf Distortion in Stachytarpheta jamaicensis in Taiwan

Abstract

Stachytarpheta jamaicensis, a traditional herbal pharmacological plant in the Family Verbenaceae that produces purplish-blue flowers, is mainly used as a garden plant in tropical and subtropical areas, including Taiwan. A begomovirus, stachytarpheta leaf curl virus (StaLCV) that caused disease on S. jamaicensis, has been reported (Xiong et al. 2005). In 2021, five symptomatic plants with mild mottle and leaf distortion (Fig. S1A, B) and three asymptomatic plants were collected in Taichung City, Taiwan. Polymerase chain reaction (PCR) and reverse transcription (RT)-PCR assays using degenerate primer pairs with expected amplicon sizes of 1.2-1.3 kb (PAL1v1978/PAR1c715; Rojas et al. 1993), 312 bp (dTospo-F2/dTospo-R2; Huang et al. 2018), and 600-750 kb (Hrp5/Pot1; Chen et al. 2006, Colinet and Kummert 1993) for Begomovirus, Orthotospovirus, and Potyvirus, respectively were performed using total DNA and total RNA plant extracts. Results showed the expected fragments were only amplified from the 5 symptomatic plants using Potyvirus degenerate primers. Three out of five randomly picked amplicons, coding the 3'-end of nuclear inclusion b protein (NIb) and 5'-end coat protein (CP) genes, were cloned and sequenced with the ABI3730 automatic sequencer (Applied Biosystems, Hammonton, NJ, USA) in Biotechnology Centre DNA-sequencing facility at National Chung Hsing University (NCHU). After NCBI BLASTN analysis, the sequences were shown to be most closely related to bidens mottle virus (BiMoV). The nucleotide sequence identities analyzed using the CLUSTAL W Methods of MegAlign program (DNASTAR, Inc., Madison, WI, USA), showed the three amplicons shared 95.8-99.8% to each other and 94.3-97.1% with 18 BiMoV isolates available in NCBI GenBank. Further RT-PCR with a specific primer (FJJ2021-278) designed from the CP of previously amplified amplicons, paired with oligo d(T) primer, were used for amplification of the 3'-CP gene and 3'-untranslated region (UTR) from total RNAs purified from symptomatic plants. The full-length CPs (804-nt and 268-aa) of the BiMoV isolates described here (Acc. Nos. OM406329 and OM406330; designated as isolate Stachy3 and Stachy7, respectively) shared 96.5-98.5% nucleotide and 97.8-99.3% amino acid identity to other BiMoV isolates. The isolate used for back-inoculation to S. jamaicensis was selected after the completion of triple single chlorotic local lesion isolation in Chenopodium quinoa. Two mechanically-inoculated S. jamaicensis plants exhibited symptoms 14-16 days post-inoculation similar to those observed in field plants and tested positive in RT-PCR using BiMoV-specific primers. In transmission electron microscopy, crude sap extracted from mechanically-inoculated C. quinoa and stained with uranyl acetate (UA) revealed flexuous filamentous virions of approximately 720 × 12 nm (Fig. S1C). A western blot assay using BiMoV antiserum (Chen and Lee 2012) revealed bands of about 34 KDa only from the mechanically-inoculated C. quinoa and the five symptomatic S. jamaicensis plants collected from the field. Taken together, we believe this is the first report of BiMoV infecting and causing mild chlorotic mottle and leaf distortion on S. jamaicensis. S. jamaicensis may serve as a new alternative host of BiMoV that can spread the disease, and consequently may directly impact the producers of horticultural or economical crops, such as lettuce, calendula, sunflower, lisianthus, and garland chrysanthemum in Taiwan.