Recent studies on Meloidogyne chitwoodi and M. fallax n. sp.
In 1992, field experiments were conducted near Baexem (south east of the Netherlands) on host suitability of Meloidogyne chitwoodi (EPPO A2 quarantine pest). It appeared that Zea mays, which is a good host for M. chitwoodi, was found there as a poor or even non-host plant. Further studies conducted on several populations of M. chitwoodi and M. hapla ;using isoenzyme polymorphism showed that five populations of M. chitwoodi from localities in the south-eastern part of the country presented different patterns from other populations of ;M. chitwoodi and M. hapla (Van Meggelen et al., 1994). The possible occurrence of a new race of M. chitwoodi was then suggested (B-type). By re-examining carefully the nematodes and especially the second stage juveniles, morphological and biological differences could also be found between these B-type populations and M. chitwoodi paratypes. It was also demonstrated that M. chitwoodi B-type was different from other Meloidogyne species. Therefore, it was proposed to consider it as a new species, called Meloidogyne fallax n. sp. (Karssen, 1996). In addition, molecular studies using PCR (with primers amplifying ribosomal intergenic spacer) confirmed these results by differentiating between M. fallax, M. chitwoodi and M. hapla (Petersen ; Vrain, 1996). These techniques also provide a useful tool for species identification.
So far, the known distribution of M. fallax is restricted to the south-eastern part of the Netherlands, near the Belgian and German borders, and, in this region is adjacent to that of M. chitwoodi. In this region, the two species are of economic importance on potatoes, black salsify (Scorzonera hispanica) and carrots. Concerning potato cultivars, it has previously been observed that on 20 cvs of potatoes tested, the percentage of tubers showing symptoms ranged from 3 to 21 %, and that the cv. Hansa and Bintje were the most susceptible. Studies on host suitability, in greenhouse and field conditions, have been conducted to identify possible rotation alternatives and to reduce nematode populations (Brinkman et al., 1996). It appeared that Phaseolus vulgaris (except the cv. Masai) supported high populations of M. chitwoodi but was not a good host for M. fallax. Chicory cultivars (Cichorium intybus), dalhia (cv. Vuurvogel) and borage (Borago officinalis) supported low populations of both M. chitwoodi and M. fallax, and can offer alternative in crop rotations. However, further studies are necessary to collect more information on crops to be used in rotation to reduce nematode populations.
Sources
Brinkman, H.; Goossens, J.J.M.; Van Riel, H.R. (1996) Comparative host suitability of selected crop plants to Meloidogyne chitwoodi Golden et al. 1980 and M. fallax Karssen 1996.
Anzeiger für Schädlingskunde Pflanzenschutz Umweltschutz, 69(6), 127-129.
Karssen, G. (1996) Description of Meloidogyne fallax n.sp. (Nematode: Heteroderidae), a root-knot nematode from The Netherlands.
Fundamental and Applied Nematology, 19(6), 593-599.
Petersen, D. J.; Vrain, T.C. (1996) Rapid identification of Meloidogyne chitwoodi, M. hapla and M. fallax using PCR primers to amplify their ribosomal intergenic spacer.
Fundamental and Applied Nematology, 19(6), 601-605.
Van Meggelen, J.C.; Karssen, G.; Janssen, G.J.W.; Verkerk-Bakker, B.; Janssen, R.; (1994) A new race of Meloidogyne chitwoodi Golden, O'Bannon, Santo & Finley, 1980 ?
Fundamental and Applied Nematology, 17(1), 93-96.