First Report of <i>Meloidogyne graminicola</i> on Rapeseed in Hubei Province of China

Meloidogyne graminicolais is a major agricultural pathogen that primarily infects Poaceae plants, such as rice, and causes considerable economic losses in China (Torrini et al. 2020). In October 2024, rapeseed root samples (Brassica napus) were collected from different farmland plots in Jingzhou City, Hubei Province. The roots of these plants had root knots of various sizes, mainly concentrated at the root tips. Females and eggs of Meloidogyne sp. were observed inside the galls, enclosed within root tissues without rupturing the surface. Second-stage juveniles (J2s) hatched and developed within the same galls. Morphological and molecular analyses of females and J2s identified the species as M. graminicola, consistent with earlier descriptions (Golden et al. 1965; Htay et al. 2016). The perineal patterns of three females were oval to nearly circular, with smooth, dense striae encircling the perineum and generally lacking patterns in the genital area. Morphometrics of 15 J2s (range, mean ± SD) were: body length (420.1 to 502.2 μm, 460.2 ± 27.5 μm); stylet (11.5 to 13.0 μm, 12.2 ± 0.4 μm) with hook-shaped basal knobs; maximum body width (16.9 to 20.1 μm, 18.9 ± 1.3 μm); hyaline tail terminus (18.5 to 24.2 μm, 21.0 ± 2.7 μm). Tails exhibited a clavate terminus. DNA extracted from four individual J2s was subjected to PCR using the species-specific primers Mg-F3 (5′-TTATCGCATCATTTTATTTG-3′) and Mg-R2 (5′-CGCTTTGTTAGAAAATGACCCT-3′) for M. graminicola a 369 bp fragment was amplified from all samples, confirming their identity as M. graminicola. Additionally, the ITS-rDNA sequences, amplified with primers TW81 (5′-GTTTCCGTAGGTGAACCTGC-3′) and AB28 (5′-ATATGCTTAAGTTCAGCGGGT-3′) (Maafi et al. 2003), showed 99% identity with reference sequences of M. graminicola (GenBank Accession No. KR604742). In greenhouse trials, ten 5-day-old semi-winter rapeseed (B. napus Zhongshuang 11) were transplanted into tubes with a 1:1 sand-soil mixture and inoculated with 200 J2s of M. graminicola. Two non-inoculated plants served as controls. After 20 days, all inoculated plants showed hook-shaped galls containing numerous J2s and eggs, matching field symptoms. No galls were observed on control plants. Re-isolated J2s from inoculated rapeseed were confirmed as M. graminicola via species-specific primers and morphological traits. To assess the M. graminicola susceptibility of different rapeseed varieties, seven cultivars (Huayou 98, Zhongshuang 11, Xiwang 129, Huayouza 62R, Zhongyou 821, Dadi 199, and Huayouza 62) were inoculated with 500 J2s per seedling. For these cultivars, the average gall number per plant was 27, 18, 15, 10, 16, 18 and 18, respectively, and the number of nematodes in roots per plant was 131, 41, 54, 26, 69, 57, and 107, respectively. All cultivars supported complete nematode invasion, colonization, and development, with galls and nematodes confirming varying susceptibility levels among varieties. To our knowledge, this is the first report of M. graminicola infecting rapeseed.