Morphological and molecular characterization of a new root-knot nematode, Meloidogyne limonae n. sp. (Nematoda: Meloidogynidae) parasitizing lemon in China

Abstract

Root-knot nematodes of the genus Meloidogyne parasitize the roots of thousands of plants and can cause severe damage and yield loss. Here, we report a new root-knot nematode, Meloidogyne limonae n. sp., parasitizing “lemon” (Citrus limon) in Hainan Province, South China. Lemon trees infected by the root-knot nematode showed poor-quality lemons, chlorosis of foliage, weak growth, and numerous root galls with white females and egg masses protruding outside. Phylogenetic trees of sequences within the ribosomal and mitochondria DNA demonstrated that this species differs clearly from other previously described root-knot nematodes. Morphologically, the new species is characterized by an oval-shaped perineal pattern and the lateral field marked by a ridge of cuticle on one or both sides, the dorsal arch is low with fine to coarse, smooth cuticle striae, vulva slit centrally located at the unstriated area; spicules of males are arcuate, curved ventrally; gubernaculum is distinct and curved; labial disc of second-stage juveniles is prominent and dumbbell-shaped; stylet knobs oval and sloping backwardly; pharyngeal glands not filling the body cavity, overlapping intestine ventrally; conical tail gradually tapering. Phylogenetic trees based on ITS1-5.8S-ITS2, D2-D3 of the 28S rDNA, and the COI and COII-16S rRNA genes of the mtDNA showed that Meloidogyne limonae n. sp. belongs to an undescribed root-knot nematode lineage that is separated from other species with the resemblance in morphology, such as M. floridensis M. hispanica, M. acronea, and M. paranaenis.