Intraspecific variability and genetic structure in Meloidogyne chitwoodi from the USA

in Nematology
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Meloidogyne chitwoodi is a quarantine pathogen and a severe problem of potato. Intraspecific variation and genetic structure are not well characterised for M. chitwoodi, but are critical to avoid misidentification and to optimise management strategies. The objective of this study was to analyse the morphological and molecular variation of four M. chitwoodi isolates, representing all races and pathotypes currently known in the USA. Despite statistically significant morphological variation among adult females, morphometrics were not able reliably to distinguish M. chitwoodi isolates. In contrast to morphology, molecular traits that are determined by nuclear ribosomal genes were stable across all isolates. Malate dehydrogenase, esterase and superoxide dismutase isozyme phenotypes were conserved in all isolates, which is an important finding for diagnostics. To gain insight into the genetic structure of M. chitwoodi, we analysed a mitochondrial DNA segment including a partial region of COII, tRNA-His and 16S rRNA genes. Genetic structure was weak and marked by high haplotype and low nucleotide diversity. We found a high level of mitochondrial heteroplasmy in M. chitwoodi. Taken together, our results indicate that there is significant intraspecific morphological and molecular variation in M. chitwoodi. Consequences for resistance breeding in potato and directions for phylogeographic studies to trace the origin of M. chitwoodi are discussed.


International Journal of Fundamental and Applied Nematological Research



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  • Photomicrographs of perineal patterns of females from four isolates representing distinct races and pathotypes of Meloidogyne chitwoodi. WAMC1 (A-D), WAMCRoza (E-H), WAMC27 (I-L), CAMC2 (M-P). (Scale bar = 10 μm).

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  • Photomicrographs of perineal patterns of Meloidogyne chitwoodi showing punctations (arrows) at the tail terminus (Scale bar: A, B = 25 μm). Punctations were found in all isolates studied. Shown here are representative patterns from isolates CAMC2 (A, C) and WAMCRoza (B, D). Panels C, D show enlarged regions of A, B.

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  • Canonical discriminant analysis performed with five morphometric variables (Table 2) in females from four Meloidogyne chitwoodi isolates representing distinct races and pathotypes. Enlarged symbols indicate means. This figure is published in colour in the online version of this journal, which can be accessed via

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  • Isozyme phenotypes from females of four Meloidogyne chitwoodi isolates representing distinct races and pathotypes. A: Malate dehydrogenase; B: Esterase; C: Superoxide dismutase. WAMC1 (R1), WAMCRoza (RO), WAMC27 (R2), CAMC2 (CA); M. javanica (MJ) as relative size marker.

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  • PCR amplification products for 194/195 primers using bulk DNA from four Meloidogyne chitwoodi isolates representing distinct races and pathotypes. WAMC1 (R1), WAMCRoza (RO), WAMC27 (R2), CAMC2 (CA), M. hapla (MH), negative control (neg). X = 1 kb DNA ladder (NEB), Y = 100 bp DNA ladder (NEB).

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  • Minimum-spanning haplotype network based on sequence variation in the COII-16S rRNA mtDNA region from four Meloidogyne chitwoodi isolates representing distinct races and pathotypes. Network combines haplotypes found across all isolates. Sizes of circles are proportional to haplotype frequency. WAMC1 (R1), WAMCRoza (RO), WAMC27 (R2), CAMC2 (CA). This figure is published in colour in the online version of this journal, which can be accessed via

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  • Isolate-specific minimum-spanning haplotype networks based on sequence variation in the COII-16S rRNA mtDNA region from four Meloidogyne chitwoodi isolates representing distinct races and pathotypes. WAMC1 (R1), WAMCRoza (RO), WAMC27 (R2), CAMC2 (CA). Colours represent each of the eight individual second-stage juveniles used for the analysis. Five sequences were analysed for each individual. Sizes of circles are proportional to haplotype frequency. Haplotype numbers correspond to Figure 6. This figure is published in colour in the online version of this journal, which can be accessed via

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