First Report of Turnip Mosaic Virus Strain Infecting Pak Choi in China

Pak choi (Brassica rapa subsp. chinensis), a widely cultivated non-heading Chinese cabbage, is an economically important crop in China. In September 2024, pak choi was cultivated on approximately 7,000 hectares in Zhangye City (100.45°E, 38.93°N), Gansu Province, China. One month after planting, plants developed symptoms including leaf mottling, wilting, and growth stunting (Supplementary Fig. 1). This infection resulted in yield losses exceeding 50%. The symptomatic presentation was consistent with Turnip mosaic virus (TuMV) infection, which was confirmed through phenotypic assessment. To characterize the TuMV strain, symptomatic pak choi plants were collected from the field for RNA extraction and molecular analysis. The TuMV genome encodes ten proteins (P1, HC-Pro, P3, 6K1, CI, 6K2, VPg, NIa, NIb, CP) (Walsh et al., 2002). Virus-specific primers designed in this study (Supplementary Table 1) were employed to amplify, clone, and sequence the viral genomic regions. The complete TuMV genome (9,798 nucleotides) was assembled and designated as the GSZY01 strain (Gan Su Zhang Ye 01). The sequence was deposited in the NCBI database under accession number PQ963938. BLAST analysis revealed that GSZY01 shares 97.15% nucleotide identity with the TuMV strain CHSC2A (LC537518.1), previously reported in Japan (Kawakubo et al., 2021). This study represents the first report of the GSZY01 strain infecting pak choi in China. Phylogenetic analysis included 30 TuMV strains with genomic sequences showing 95.70%–97.15% similarity to GSZY01 (Supplementary Fig. 2). The phylogenetic tree (Supplementary Fig. 3) confirmed that CHSC2A is the closest genetic relative of GSZY01, while other analyzed strains formed distinct clusters. The pathogenicity of GSZY01 was assessed on Nicotiana benthamiana plants. Four-leaf-stage seedlings were mechanically inoculated with either GSZY01 or the reference strain TuMV C4 (Li et al., 2019). The experiment comprised three biological replicates with 10 plants each, totaling 30 plants per treatment. At 7 days post-inoculation (DPI), 83.33% (25/30) of GSZY01-inoculated plants exhibited symptoms including leaf necrosis, chlorosis, and petiole wilting. In contrast, TuMV C4 exhibited significantly stronger pathogenicity, causing wilting and necrosis in most inoculated leaves and severely impairing plant development. By 12 DPI, all TuMV C4-infected plants had died, whereas GSZY01-infected plants, although significantly smaller than controls, continued to grow (Supplementary Fig. 1). Total RNA was extracted from the plants inoculated with GSZY01. Following reverse transcription, the ten TuMV genes were amplified by PCR and verified through Sanger sequencing. Subsequent analysis of the viral strain identified it as GSZY01. These findings indicate that GSZY01 is less virulent than TuMV C4. Nevertheless, its pathogenicity necessitates monitoring to prevent substantial crop losses.