First Report of root-knot nematode <i>Meloidogyne hapla</i> Infecting <i>Taraxacum mongolicum</i> in Hubei Province, China

Taraxacum mongolicum is valued both as a nutritious edible plant and a medicinal herb with anti-inflammatory and antimicrobial properties, and it is being explored as a potential natural antibiotic alternative in livestock farming (Wang et al. 2022). In September 2025, a field survey of root-knot nematodes was conducted in T. mongolicum cultivation gardens in Xuan'en County, Hubei Province, China (30°5'49" N; 109°48'14" E; altitude 1425 m). Approximately 60% of plants inspected across three surveyed gardens (with an estimated total of over 500 plants) showed varying degrees of above-ground decline, including stunting, chlorosis, and wilting under water stress. Subsequent root examination confirmed that all symptomatic plants exhibited characteristic root galling. The most pronounced symptom was numerous small galls or knots on the fibrous root. Females and eggs were dissected from galled roots, and second-stage juveniles (J2s) and males were extracted from the rhizosphere soil for morphological and species identification. The perineal patterns of mature females (n=20) displayed a distinctive high, squarish dorsal arch with smooth to wavy striae. The lateral lines were indistinct, which divided the pattern into two distinct areas. Morphological measurements of females (n = 20) were as follows: body length (L) = 798.0 ± 53.6 μm, body width (BW) = 468.7 ± 50.2 μm, stylet length (ST) = 15.0 ± 0.62 μm, dorsal pharyngeal gland orifice to stylet base (DGO) = 5.12 ± 0.24 μm, and vulval slit length = 23.4 ± 1.36 μm. Measurements of J2s were as follows: L = 384.06 ± 16.32 μm, BW = 16.25 ± 1.42 μm, ST = 12.01 ± 0.84 μm, DGO = 2.93 ± 0.68 μm, tail length = 52.64 ± 11.68 μm, and hyaline tail terminus = 10.98 ± 2.56 μm. These morphological characteristics were consistent with those of Meloidogyne hapla Chitwood, 1949, as described by Whitehead (1968). For molecular confirmation, DNA was extracted from single females (n=5) obtained from different field-collected plants. The 28S rDNA D2/D3 region and the variable V3 and V5 regions of the 18S rDNA were amplified using primers MF/MR (5'-GGGGATGTTTGAGGCAGATTTG-3', 5'-AACCGCTTCGGACTTCCACCAG-3') (Hu et al. 2011) and primers 18sf1/18sr1 (5´-CGCAAATTACCCACTCTC-3´/5´AGTCAAATTAAGCCGCAG-3´) (Waite et al. 2003). The obtained sequences (GenBank accession no. PX928920 and PX927953, respectively) showed 99.79-100% identity with multiple confirmed M. hapla sequences in the NCBI database (PQ284214 and MK102780 sequences, respectively.). To confirm the pathogenicity of the population, ten 4-week-old healthy T. mongolicum seedlings cultured in sterilized sand were each inoculated with 2,000 J2s hatched from egg masses. Six noninoculated seedlings served as negative controls. After maintenance at 22°C for 60 days under greenhouse conditions, root galling symptoms identical to field observations developed on all inoculated plants, while six non-inoculated controls remained asymptomatic. The reproduction factor (final population density / initial inoculum density) was calculated to be 7.6 ± 1.1 (mean ± SE, n=5), demonstrating successful reproduction on the new host. The nematodes re-isolated from the galls were confirmed to be M. hapla by PCR with species-specific SCAR primers JMV1/JMV hapla (5'-GGATGGCGTGCTTTCAAC-3'/5'-AAAAATCCCCTCGAAAAATCCACC-3') (Dong et al. 2015), yielding a 438 bp amplicon (PX939355). To our knowledge, this is the first report of M. hapla infecting T. mongolicum. This finding highlights a new potential threat to dandelion production for growers and agricultural practitioners. Further studies are needed to assess the economic impact and develop management strategies for this disease.