First Report of <i>Meloidogyne incognita</i> Infecting <i>Polygonum fagopyrum</i> and <i>Acroglochin persicarioides</i> in Guizhou, China

In September 2024, root galls accompanied by leaf yellowing and stunted growth were observed on Polygonum fagopyrum (a medicinal plant and common weed, with an infestation rate as high as 60–70% as a dominant species) and Acroglochin persicarioides (primarily used as livestock feed and also a widespread weed, demonstrating an infestation rate of approximately 70% despite a smaller sample size) growing near root-knot nematode-infected tobacco plants in an approximately 0.67- hectare area of Weining County (27°16′N, 104°39′E), Guizhou Province, China. To identify the causal agent, root galls from both plants were collected, stained using Duan's (2011) method, and dissected to isolate females and egg masses. Second-stage juveniles (J2) were obtained after surface sterilization and incubation at 28 °C. Morphometric analysis of females from P. fagopyrum (n=10) and A. persicarioides (n=10) showed body lengths (BL) of 501.2–720.1 μm and 498.1–718.6 μm, and stylet lengths (ST) of 14.1–16.9 μm and 13.7–16.4 μm, respectively. J2 specimens (n=30 per host) exhibited similar measurements: BL 327.6–415.1 μm (P. fagopyrum) and 321.5–416.3 μm (A. persicarioides), body width (BW) 13.2–16.7 μm and 12.8–15.9 μm, ST 9.5–12.8 μm and 9.1–12.5 μm, dorsal gland orifice (DGO) 2.1–3.5 μm and 1.9–3.3 μm, and tail lengths of 38.3–54.5 μm and 35.9–53.8 μm, respectively. Females displayed a perineal pattern with a high, square-shaped dorsal arch and indistinct lateral lines, consistent with Meloidogyne incognita (Eisenback & Hirschmann, 1981). Molecular identification was conducted using DNA extracted from ten females per host with the species-specific primers MiF/MiR for M. incognita (Meng et al. 2004), Far/Rar for Meloidogyne arenaria (Zijlstra et al. 2000), Fjav/Rjav for Meloidogyne javanica (Zijlstra et al. 2000), and Fha/Rha for Meloidogyne hapla (Dong et al. 2001) were used, with M. incognita from Prof. Yang Wang's research group as positive controls and water as negative controls. A 955 bp amplicon was amplified only with M. incognita primers. Sequencing (GenBank accessions PQ885373.1 for P. fagopyrum and PV820717.1 for A. persicarioides) confirmed 99.7% (683/685 bp) and 100% (817/817 bp) identity with M. incognita references OR469000.1 and KP234265.1, respectively. Pathogenicity was confirmed in greenhouse trials. For each plant species, approximately three-week-old healthy plants grown in sterilized soil were inoculated. Each pot received approximately 1000 J2 larvae hatched from egg masses (15 pots per species), with five non-inoculated pots serving as controls. After 50 days at 28°C, all inoculated plants developed root galls, while controls remained symptom-free. Re-isolated nematodes were confirmed as M. incognita based on morphology and PCR. Polygonum fagopyrum and Acroglochin persicarioides are common weeds in tobacco fields. Although valued as a medicinal plant and cultivated for livestock feed, respectively, their presence as weeds in agricultural settings can serve as alternate hosts for Tobacco mosaic virus (TMV), Cucumber mosaic virus (CMV), and Potato virus Y (PVY). This is the first report of M. incognita infecting these species in China, highlighting their potential role as nematode reservoirs that may exacerbate damage to tobacco. Increased field monitoring and management are recommended to reduce their impact on tobacco production.