First report of Meloidogyne fallax parasitising coriander in the United Kingdom

Stunted coriander (Coriandrum sativum L.) plants were found in a commercial farm in Feltwell, Norfolk, United Kingdom. Roots were poorly developed and presented atypical, often small, hard-to-notice galls (Fig. S1A). Before coriander, potatoes and turf were grown in the same area. The infested soil was collected and transferred to the Crop Science Centre (Cambridge, UK) along with stunted turf plants from the same area. Extraction and examination of turf roots revealed Meloidogyne females. The Meloidogyne population was bulked up by growing tomato, potato and wheat in this infested soil under growth-chamber conditions (21°C, 16h/8h, day/night). Ten females were collected from these plants for morphological characterisation. They exhibited a variable perineal pattern, either rounded or oval-shaped, both of which presented a moderate-to-high dorsal arch and thick striae that were slightly or moderately wavy (Fig. S1B1 to B3). Females were small, globular to pear-shaped (Fig. S1C). These characteristics were consistent with Meloidogyne fallax and M. chitwoodi (EPPO, 2013). To clarify species identity, molecular identification was performed using ITS primers (Ye et al., 2019). Single females were randomly handpicked from roots, transferred to lysis buffer and cut and digested (Sonawala et al., 2024). PCR was performed using 5 μl of the digested sample with KOD Xtreme polymerase (Sigma-Aldrich) using an initial denaturation at 94°C for 2 min; 40 cycles of 98°C for 10 s, 55°C for 30 s and 68°C for 1 min. The purified PCR products (Monarch® Gel Extraction Kit) were Sanger-sequenced. Sample sequences along with publicly available Meloidogyne spp. sequences from GenBank were aligned using MAFFT with L-INS-i algorithm (Katoh & Standley, 2013). Alignments were manually inspected, and ambiguously aligned flanking regions were trimmed in Geneious (2026.1.1). A maximum-likelihood phylogenetic tree was inferred using IQ-TREE v. 3.0.1 (Wong et al., 2026), with the best-fit substitution model selected using ModelFinder (Kalyaanamoorthy et al., 2017). Branch supports were assessed using SH-aLRT (1,000 replicates). Phylogenetic analysis confirmed the identity of the samples as Meloidogyne fallax (Figure 2). To determine the host status of coriander, 5 pots containing 3 plants each were inoculated with 500 nematodes (eggs+J2s) and 60 days after inoculation, they were extracted. We confirmed coriander susceptibility: the reproduction factor (Final population/Initial population, susceptible if > 1) ranged from 1.45 to 41.5 (average = 11.9). Nematodes per gram of root ranged from 20 to 400 (average = 116). Consistent with field observations, inoculated plants showed inconspicuous galls (Fig. S1D), which required careful examination under a microscope. The same phenotype was also observed in inoculum plants (tomato, wheat and potato), in which females were present within atypical galls or swollen root tissue (Fig S1E), similar to that observed for other species (e.g. M. incognita or M. javanica). Meloidogyne fallax was a quarantine root-knot species, later reclassified as present with limited distribution in the UK (Barker et al., 2024). However, the lack of evident or distinguishable root symptoms possibly constrains further reports in new hosts and/or geographies. Our work underscores the importance of M. fallax to UK agriculture and, to our knowledge, this is the first report of M. fallax damaging coriander.