A New Root-Knot Nematode species, Meloidogyne karsseni n. sp. (Nematoda: Meloidogynidae), From Mexico and a Taxonomic Update on M. paranaensis From Guatemala

Abstract

A new root-knot nematode (RKN) species, Meloidogyne karsseni n. sp., associated with sweet pepper from Mexico, and a population of M. paranaensis from Guatemala, are described using data from morphological, biochemical (isozyme enzymes), molecular, and phylogenetic analyses. Meloidogyne karsseni n. sp. can be morphologically diagnosed using the combined features of the second-stage juveniles, viz. body length (345 to 422 μm), a conical rounded head region, a post-labial annule lacking transverse striation, a thin stylet 11 to 12 μm long, rounded to oval and backwardly sloping knobs, dorsal gland orifice (DGO) at 5.2 to 6.0 μm from the knobs, a hemizonid just above the secretory-excretory (SE) pore, a tapering tail with finely rounded terminus and one or two very weak constrictions at hyaline tail tip; the female characters viz. oval-to-rounded perineal pattern with coarse striation on lateral sides around the anus, low dorsal arch with finer striations, and distinctly visible lateral lines; and the male characteristics viz. a rounded and continuous head, a post-labial annule without transverse striations, a robust stylet 20 to 24 μm long, rounded-to-oval and slightly backwardly sloping knobs, and a DGO at 2.4 to 2.9 μm from the knobs. In all the studied males of M. paranaensis, a characteristic sclerotization around the duct of SE-pore was also observed for the first time. Sequences of 18S, D2-D3 of 28S, and ITS of rDNA, and cox1 of mtDNA were generated for the two species, and in the phylogenetic trees based on these genes, both species appeared in the tropical RKN species complex clade.

Keywords: Guatemala; Meloidogyne; Mexico; Root-knot nematode; new species; phylogeny; taxonomy.

Figure 1:

Light and scanning electron microscopy images of Meloidogyne karsseni n. sp. second-stage juveniles (J2). A, B: Anterior body up to pharyngeal gland end showing hemizonid (h) and secretory-excretory pore (se); C–F: Anterior end showing lip region, stylet and dorsal gland orifice (dgo); G–J: En face views; K–O: Posterior body showing rectum (r), anus (a), tail and hyaline part of tail.

Figure 2:

Light and scanning electron microscopy images of Meloidogyne karsseni n. sp. A, E: Whole body of female; B, C: En face of females; D: Neck region of female showing stylet and bulb; F–L: Female perineal patterns (G: outside view of cuticle; H: view from inside of cuticle); M–P: Anterior body of male showing lip region, stylet and dorsal gland orifice; Q: En face view of male; R–T: Posterior body of male showing spicules.

Figure 3:

Line illustrations of Meloidogyne karsseni n. sp. A: Anterior body of second-stage juveniles (J2) showing up to gland end; B: En face view of J2; C: Anterior end of J2 showing stylet and dorsal gland orifice; D, E: Posterior end of J2; F: Whole body of female; G: Neck region of female; H: Female perineal pattern; I: Anterior body of male; J: En face view of male; K, L: Posterior body of male.

Figure 4:

Light microscopy images of Meloidogyne paranaensis. A–C: Anterior body of second-stage juveniles (J2) showing lip region, stylet, knobs and dorsal gland orifice (dgo); D, E: Secretory-excretory (se) pore and hemizonid (h) of J2; F, G: Posterior body of J2 showing inflated rectum (r), tail and tip; H: Whole body of female; I, J: Anterior body of females showing stylet, knobs and mid-bulb of pharynx; K–N: Perineal patterns of females and anus (a) (K, L: outside view of cuticle; M, N: view from inside of cuticle); O–R: Anterior body of males showing lip region, stylet, knobs, dorsal gland orifice, secretory-excretory pore and hemizonid; S, T: Cuticular thickenings at secretory-excretory pore of males; U, V: Posterior body of male showing spicules and gubernaculum.

Figure 5:

Scanning electron microscopy images of Meloidogyne paranaensis. A: Anterior body of second-stage juveniles (J2) showing lip region; B–D: En face views of J2 showing oral openings, labial disc, amphids, post-labial annule with incomplete transverse striations; E: Mid-body of J2 showing four lateral lines forming three bands; F: Posterior body of J2 showing tail and tip; G, H: Perineal patterns of females; I: Anterior body of a male showing lip region; J, K: En face view of males showing oral openings, labial disc, amphids and post-labial annule; L: Posterior body of male; M: Mid-body of a male showing four lateral lines forming three areolated bands.

Figure 6:

Line illustrations of Meloidogyne paranaensis. A, B: Anterior body of second-stage juveniles (J2); C: En face view of J2; D, E: Posterior body of J2; F: Whole female bodies; G: Anterior body of female; H: Perineal pattern of female; I: Anterior body of male; J: Cuticular thickenings of duct near secretory-excretory pore of male; K: Twisted tail of male showing spicules and gubernaculum.

Figure 7:

Phylogenetic relationships of Meloidogyne karsseni n. sp. (green) and M. paranaensis (blue) with other Meloidogyne spp. based on the Bayesian analysis of the D2–D3 of 28S rDNA sequence alignment using the GTR + I + G nucleotide substitution model. Posterior probabilities of more than 0.5 are given for appropriate clades. Tropical Meloidogyne species complex is highlighted in the colored box and the M. paranaensis sequences included in Santos et al. (2020) are in bold.

Figure 8:

Phylogenetic relationships of Meloidogyne karsseni n. sp. (green) and M. paranaensis (blue) with other Meloidogyne spp. based on the Bayesian analysis of the ITS sequence alignment using the GTR + I + G nucleotide substitution model. Posterior probabilities of more than 0.5 are given for appropriate clades. Tropical Meloidogyne species complex are highlighted in colored box and the M. paranaensis sequences included in Santos et al. (2020) are in bold.

Figure 9:

Isozyme characterizations of Meloidogyne karsseni n. sp. (Mk) and M. paranaensis (Mp) young females. A: Esterase pattern, B: Malate dehydrogenase pattern of M. karsseni n. sp., C: Esterase pattern, D: Malate dehydrogenase pattern of M. paranaensis. Meloidogyne javanica (Mj) was used as a reference sample and is shown using a plus sign in the middle two positions of the gels.