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Biological and molecular characterization of citrus tatter leaf virus in Taiwan

Chun-Yi Lin: National Taiwan University

<div>Citrus tatter leaf virus (CTLV) causes chlorotic leaves with bud union incompatibility in citrus scion and its current incidence in Taiwan is 65%. However, the burden of infection has long been underestimated due to its common latency, and the serious threat of tatter leaf disease should be investigated and addressed without delay. Here, the biological characteristics and genome sequences of Taiwanese isolates are evaluated. Full-length sequencing and phylogenetic analysis of three local isolates revealed similarities with isolates from neighbouring countries, indicating their possible origins. Two mild isolates obtained from Liuchen sweet orange (LCd-NA-1) and kumquat (Kq-6-2-46) were inoculated on indicator plants and exhibited differences in foliar symptom expression and temperature tolerance compared with foreign isolates causing severe disease. Improved quantitative PCR-based detection methods using redesigned primer pairs indicated high sensitivity and specificity for both local and foreign isolates. Similar but delayed systemic symptoms were observed when wildtype virus <em>in vitro</em> transcripts generated from a full-length infectious clone of the Ponkan mandarin isolate (pCTLV-Pk-8) were inoculated on <em>Chenopodium quinoa</em>. These symptoms were unevenly distributed and highly concentrated on the inoculated sides of leaves and top leaves. A single codon mutation (U5642C) in the coat protein transcription start site in the pCTLV-Pk-8 sequence resulted in defective systemic infection, indicating a role for the coat protein in viral movement. The combination of biological assays, improved detection and infectious clone construction provides comprehensive information and a foundation for citrus virus management and further research.</div>

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