Meloidogyne

Meloidogyne

Byron J. Adams *


     ===================== M. chitwoodi 
     |
     |  ================== M. trifoliaphila 
     |  |
     |  |  =============== M. graminicola 
     |  |  |
     |  |  |  ============ M. hapla 
<<===|  |  |  |
     ===|  |  |  ========= M. mayaguensis 
        ===|  |  |
           ===|  |  ====== M. incognita 
              ===|  |
                 ===|===== M. javanica 
                    |
                    ====== M. arenaria

Adams and Powers, 1996

Containing clade(s): Meloidogyninae

Introduction

Discussion of Phylogenetic Relationships

References

Introduction

Root knot nematodes of the genus Meloidogyne have a worldwide distribution and are obligate parasites of thousands of plant species, including representative monocots, dicots, herbaceous, and woody plants. Though currently there are more than 60 species, four are major agricultural pests found in virtually all agricultural areas of the world (M. hapla, M. incognita, M. javanica, M. arenaria). M. incognita and M. javanica, which have the broadest geographic distribution and host range, are also obligate parthenogens. Other modes of reproduction in the genus include amphimixis and facultative meiotic parthenogenesis.

Because of the global distribution of the genus, it has been hypothesized that the lineage is of ancient origin. Accordingly, the origin and maintenance of obligate parthenogenesis as a mode of reproduction can be viewed as a "key innovation" to account for the historical success of the genus over the millennia. However, were this to be the case, it would be a striking exception to the trend among other metazoans in which extant unisexual lineages are typically of recent origin.

Discussion of Phylogenetic Relationships

Phylogenetic relationships among the Meloidogyne have been investigated by Adams & Powers (1996). Ingroup taxa included M. incognita, M. javanica, M. mayaguensis, M. arenaria, M. chitwoodi, M. graminicola, M. hapla, and M. trifoliaphila. Outgroup taxa were Radopholus similus and Globodera pallida. 18s and 5.8s ribosomal genes were used to establish phylogenetic relationships using a variety of treebuilding methods, sequence alignment parameters, and character optimization. All treebuilding algorithms (Parsimony, Maximum Likelihood, Neighbor Joining) produced a single phylogenetic tree which was completely resolved with the exception of M. incognita, M. javanica, and M. arenaria, which form a terminal unresolved polytomy. Although too few taxa have been sampled to thoroughly investigate any "evolutionary trends" which may appear in the clade, it clearly suggests a single origin of mitotic parthenogenesis. For example, forcing a paraphyletic origin of obligate unisexuality requires an extra 16 steps on the resulting tree. This suggests that mitotic parthenogenesis is not ancestral, but a derived reproductive strategy. Though no explicit time of divergence can be inferred from the phylogeny, it is clear that relative to the other sampled members of the group, obligate unisexuality in the genus is a recently derived mode of reproduction.

References

Adams, B.J. and T.O. Powers. 1996. A rDNA based phylogenetic 
          analysis of the genus Meloidogyne 
          suggests a recent origin of mitotic parthenogenesis 
          as a mode of reproduction. Proceedings of the Third 
          International Nematology Congress:  Origin of Meloidogyne 
          sp. and resistance genes. Guadeloupe, FWI.
Castagnone-Sereno, P., C. Piotte, J. Uijthof, P. Abad, E. Wajngberg, 
          F. Vanlerberghe-Masutti, M. Bongiovanni, and A. Da.masso. 
          1993. Phylogenetic relationships between amphimictic 
          and parthenogenetic nematodes of the genus Meloidogyne 
          as inferred from repetitive DNA analysis. Heredity 
          70:195-204.
Hugall, A., J. Stanton, and C. Moritz. 1997. Evolution of the 
          AT-rich mitochondrial DNA of the root knot nematode, 
          Meloidogyne hapla. Mol. Biol. Evol. 
          14:40-48.

About this page

Page constructed by Marcella Shaver-Adams, madams@unlgrad1.unl.edu.

Byron J. Adams
E-mail: bjadams@crcvms.unl.edu.
University of Nebraska-Lincoln, Department of Plant Pathology, 406 Plant Sciences Hall, P.O. Box 830722, Lincoln, NE 68583-0722 USA

Meloidogyne

Table of Contents

Introduction

Discussion of Phylogenetic Relationships

References

About this page