First Report of the Root-Knot Nematode (Meloidogyne incognita) Parasitizing Coriandrum sativum L. in Shaanxi Province, China

Coriander (Coriandrum sativum L.), commonly known as Chinese parsley, is an herbaceous species valued for its pharmacologically active constituents, including fatty acids, sterols, and carotenoids, with well-documented applications in traditional Chinese cuisine and medicine (Wei et al., 2019). In October 2024, symptomatic C. sativum plants exhibiting stunted growth (>85% field incidence), foliar chlorosis, and root galling were collected from an agricultural field in the Chang'an District (34°06'10"N, 108°54'07"E) of Xi'an City, Shaanxi Province, China. Macroscopic examination of infected roots showed multiple nodular formations containing white, pear-shaped adult females and associated egg masses, which were consistent with root-knot nematode (RKN) infestation. In the 10-30-cm soil layer, second-stage juveniles (J2) occurred at an average population density of 572 per 100 g of soil. Meloidogyne sp. females and egg masses were isolated from infected roots, and nematode eggs were subsequently extracted using established protocols (Wang et al. 2021; Wang and Zhang 2024) to obtain J2. Males were not readily available in this experiment. Comprehensive morphological characterization was performed on both J2 and adult females. For J2 (n = 20), they were vermiform and had a slender tail that tapered to a rounded tip with a distinct hyaline region at the tail terminus. Moreover, J2 revealed the following morphometric dimensions (mean ± SD): body length (BL) ranged from 349.92 to 422.14 (386.80 ± 24.69) μm, body width (BW) from 14.67 to 17.18 (15.83 ± 0.96) μm, stylet length (SL) from 12.87 to 16.31 (13.89 ± 1.08) μm, tail length (TL) from 38.24 to 55.56 (45.11 ± 5.01) μm, hyaline tail terminus (HTT) from 9.51 to 14.97 (12.34 ± 1.79) μm, and dorsal esophageal gland orifice to stylet base distance (DGO) from 9.80 to 14.22 (2.34 ± 0.63) μm. For adult females, the perineal pattern (n = 10) exhibited a characteristic high dorsal arch with smooth, wavy striae, while the lateral line was mostly indistinct. Additionally, morphometric measurements of females (n = 20) were as follows (mean ± SD): BL = 632.40 ± 71.68 (524.36 to 764.51) μm, BW = 418.81 ± 48.15 (345.25 to 521.49) μm, SL = 15.80 ± 1.76 (12.75 to 20.24) μm, DGO = 2.95 ± 0.51 (2.17 to 3.83) μm, vulval slit length (VSL) = 21.08 ± 2.35 (17.12 to 25.22) μm, and vulval slit to anus distance (VSAD) = 18.55 ± 1.73 (15.21 to 21.32) μm. These morphological characteristics were consistent with the taxonomic description of Meloidogyne incognita (Kofoid & White, 1919) Chitwood, 1949 (Whitehead 1968). In further species validation, genomic DNA of 10 individual adult females was extracted, and subjected to polymerase chain reaction (PCR) amplification with primers Inc-K14-F/Inc-K14-R (5’-GGGATGTGTAAATGCTCCTG-3’, 5’-CCCGCTACACCCTCAACTTC-3’) (Randig et al., 2002) for the SCAR marker gene of M. incognita and D2a/D3b primers (5’-ACAAGTACCGTGAGGGAAAGTTG-3’, 5’-TCGGAAGGAACCAGCTACTA-3’) (Ye et al., 2015) for the D2-D3 segment of 28S rDNA. Sequencing of the 372-bp PCR products (Accession: PV578840) amplified with the Inc-K14-F/Inc-K14-R primers revealed 100% identity with available sequences of M. incognita (MZ522721, OR453944, and OQ427638) in the NCBI database. Similarly, the PCR products (Accession: PV569951) amplified using the 28D3a/D3b primers were sequenced (728 bp), and showed 100% identity with M. incognita sequences (MN847618, MT197289, and OQ633455). To verify the pathogenicity and reproductive capacity of M. incognita, plants (C. sativum L. 'Aodaliya Siji') were cultivated in sterilized potting soil under standardized conditions (16-hour light/8-hour dark photoperiod, 28°C during light and 25°C during dark phases). After three weeks post-germination, uniformly healthy seedlings (n = 10) were inoculated with 500 J2 per plant using a glass pipette, while non-inoculated plants served as negative controls. At 50 days post-inoculation (dpi), root galling symptoms were clearly observed in the plants, aligning with field observations, and an average J2-reproductive factor (RF = Pf/Pi) of 3.86 was observed across all inoculated plants. On the contrary, control plants throughout the experimental period showed no detectable nematodes development. Molecular identification of nematodes was confirmed using Inc-K14-F/Inc-K14-R primers. The experiment was repeated twice with consistent results, demonstrating experimental reproducibility. M. incognita is one of most destructive crop pathogen responsible for annual crop losses worldwide (Rutter et al., 2022). In 1989, damage to coriander caused by M. incognita was described briefly in Guangxi Zhuang Autonomous Region, China, based solely on morphological characteristics (Feng et al., 1989). To our knowledge, this study provides the first documented evidence of M. incognita infecting C. sativum in Shaanxi Province, which expands the known host range of this highly polyphagous nematode in northern China. These findings offer immediate implications for refining integrated pest management protocols in C. sativum cultivation across broader regions of China, which will substantially minimize the potential economic losses in the future.