Lack of correlation between (a)virulence and phylogenetic relationships in root-knot nematodes (Meloidogyne spp.)

Abstract

In tomato, the Mi resistance gene controls the major root-knot nematode species Meloidogyne arenaria, M. incognita and M. javanica. However, resistance-breaking (i.e. virulent) biotypes have been reported from most of the tomato-growing areas in the world. In this study, we assembled a collection of 17 isolates belonging to these three species, either avirulent or virulent against the Mi gene, in order to analyze their genetic diversity and phylogenetic relationships. According to parsimony analysis, genomic fingerprints based on RAPD or AFLP markers were independently used to compute trees describing the relationships between the isolates. In both dendrograms, isolates belonging either to the M. incognita or M. javanica species appeared clustered together, which tends to indicate a monophyletic origin for each of these two species. Conversely, M. arenaria isolates were not included in one single clade, which raised questions about the taxonomic status of the currently designated species M. arenaria. Moreover, our data showed that clustering of isolates was not associated with their (a)virulence against the tomato Mi resistance gene. This lack of correlation between groups determined by molecular markers and virulence indicates that most of the observed DNA polymorphism is independent of virulence, which is presumably under host selection.