First Report of Northern Root-Knot Nematode <i>Meloidogyne hapla</i> on <i>Adenophora triphylla</i> in the Republic of Korea

Adenophora triphylla is a perennial medicinal herb in the family Campanulaceae that is widely distributed in East Asia, including Korea, Japan, China, and Taiwan. In Korea, it is commonly known as jandae, and its roots, referred to as sasam, have long been used in traditional medicine for treating respiratory disorders such as asthma, bronchitis, and cough (Lee et al., 2024). With increasing interest in health-promoting functional crops, cultivation of A. triphylla has expanded to meet growing demand that cannot be satisfied by natural harvesting alone (Lee et al., 2019). However, information on soil-borne diseases of this crop remains limited, and reports of plant-parasitic nematodes associated with A. triphylla are particularly scarce. During a survey of soil-borne diseases in A. triphylla cultivation fields in Gangwon Province, South Korea, root galls were observed at one site located at 37.319064°N, 128.850408°E, 760.22 m altitude. Affected plants showed aboveground symptoms, including leaf yellowing and reduced plant height compared with surrounding plants. Approximately 500 g of rhizosphere soil, including infected roots, was collected from affected A. triphylla plants for analysis. The population density of second-stage juveniles (J2s) was 320 individuals per 100 cm³ of soil. Approximately 30 females were isolated from galled roots. Morphological traits of females and J2s were consistent with Meloidogyne hapla Chitwood, 1949 (Whitehead 1968). Female perineal patterns were characterized by distinct punctations near the anus, a low and rounded dorsal arch, and the presence of a wing-shaped form in the lateral part. J2s isolated from the rhizosphere soil were slender and vermiform, with a pointed tail and a distinct hyaline region. Mean measurements of J2s (n = 15) were as follows: body length = 381.8 μm (353.7–411.5 μm), tail length = 41.0 μm (30.4–51.6 μm), stylet length = 12.5 μm (11.6–13.6 μm), a = 25.5 (20.2–28.1), and c = 9.5 (7.8–12.5). To further confirm the species, genomic DNA was extracted from single females (n = 10), and the D2–D3 expansion segments of the 28S rRNA gene and the internal transcribed spacer (ITS) region were amplified and sequenced using the primer sets D2A/D3B and TW81/AB28, respectively (De Ley et al. 1999, Subbotin et al. 2000). The sequences were deposited in GenBank under accession numbers PZ379519 for 28S rRNA and PZ369149–PZ369150 for ITS. BLAST analysis showed 99 to 100% identity with M. hapla sequences in GenBank, including OQ269672 for 28S rRNA and OP023955 for ITS. Bayesian phylogenetic analysis placed the isolates from A. triphylla within a strongly supported M. hapla clade. To confirm pathogenicity, a modified Koch’s postulates test was conducted under greenhouse conditions (26 ± 2°C). Adenophora triphylla plants grown in a sterile sand–clay soil mixture (9:1, v/v) were inoculated with 300 eggs per pot, with three replicates. After 12 weeks, root galls containing females and egg masses were observed on all inoculated plants, whereas no root galls were observed on non-inoculated control plants. The final population density reached 7,815 ± 612 J2s per 500 ml of soil, corresponding to a reproduction factor of 26.05. These results confirmed the pathogenicity of M. hapla on A. triphylla and indicate that A. triphylla may serve as an important host for this nematode. To the best of our knowledge, this is the first report of M. hapla infecting A. triphylla in South Korea. Given the increasing cultivation of A. triphylla as a medicinal and functional crop, regular monitoring, early detection, and integrated management of root-knot nematodes are needed to support sustainable production.