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In order to expand our understanding of the genetics of root-knot nematodes, variation in nuclear DNA and mitochondrial DNA in Meloidogyne incognita, M. arenaria and M. javanica was investigated. Despite the obligate mitotic parthenogenetic mode of reproduction, a large number of AFLP polymorphisms were observed among all 16 populations studied. Both UPGMA and principle coordinate analyses revealed three distinct groups that corresponded with the respective species identities of the 16 populations. M. incognita was genetically most distinct. Amplification of 63-bp tandem repeats (TR) in mtDNA from single individuals enabled the calculation of diversity measures at three hierarchical levels: within individuals, among individuals of a single population and among populations. For all three species, the highest diversity was observed within individuals explaining 43–65% of the total diversity. Many individuals contained more than one mtDNA size variant. M. incognita harboured the most heteroplasmic individuals and was the most homogenous at the population level. Only 13% of the total diversity was observed among populations, while this figure was 35% for M. arenaria. Both TR and AFLP data showed that M. arenaria is the most heterogeneous species. The comparison of the genetic distances based on AFLPs and mtDNA size variants revealed a significant correlation for the six M. arenaria populations, whereas no consistent correlation was observed for the populations of the other two species. |
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