Intraspecific variability and genetic structure in Meloidogyne chitwoodi from the USA

Abstract

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 aU 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.

Intraspecific variability of the facultative meiotic parthenogenetic root-knot nematode (Meloidogyne graminicola) from rice fields in Vietnam

“…[23,33]. However, the polymorphism of these markers is limited in comparison with mitochondrial DNA markers [4,48]. Recent studies suggest that nucleotide variations could be found in sequences from the M. graminicola mitochondrial amplification product ( [49]; Bellafiore et al, unpublished data).…”

“…The Meloidogyne genus therefore appears as a model system to investigate the impact of each reproduction system on the maintenance of genetic diversity and intraspecific variability in correlation to the pathogenicity [3]. For instance, M. chitwoodi, a meiotic parthenogenetic nematode, has a wide host range and has shown to have significant intraspecific variability and genetic structure between four populations from the USA [4]. In addition, several obligatory mitotic parthenogenetic nematodes having a larger host range were studied (e.g., M. enterolobii), and were characterized by a genetically homogeneous organization [5].…”

Morphological variability in second-stage juveniles and males of Meloidogyne chitwoodi

“…Meloidogyne chitwoodi isolates studied include WAMCl (race 1), WAMCRoza (race 1, pathotype Roza), WAMC27 (race 2), and CAMC2 (race 2, pathotype California) (Brown et al, 2009;Humphreys-Pereira & Elling, 2013). Nematodes were propagated on tomato cv.…”

“…As part of the same study, we analysed the genetic diversity of M. chitwoodi based on mitochondrial DNA and found that this nematode is very heteroplasmic. Distinct isolates showed a weak genetic structure, indicative of gene flow and sexual reproduction between populations under field conditions or a common founder population (Humphreys-Pereira & Elling, 2013). This is an important finding because exchange of genetic material between M. chitwoodi populations in the field could explain isolate-specific variability in virulence.…”

“…We have provided extensive morphological data for adult M. chitwoodi females from different isolates and found significant intraspecific morphological variability (Humphreys-Pereira & Elling, 2013). However, comparable data for second-stage juveniles (J2) and males are lacking.…”