Nine populations of Meloidogyne spp. from Greece have been identified as M. javanica or M. incognita using either isozyme phenotypes or the sequence characterized amplified region-polymerase chain reaction (SCAR-PCR) technique. Virulence against the Mi resistance gene was assayed by pot experiments in controlled conditions and revealed the ability of five populations of M. javanica and one population of M. incognita to reproduce on tomato cultivars containing that gene. A resistance-breaking population of M. incognita is reported for the first time in the country; the M. javanica populations constitute new records for the Greek mainland.Resistance in commercially grown tomato hybrids to root knot nematodes (RKN, Meloidogyne spp.) is conferred by the Mi gene which is effective against M. javanica, M. incognita and M. arenaria at moderate soil temperature (Williamson, 1998). However, there are several reports of virulent populations of these Meloidogyne species on resistant tomato cultivars occurring either naturally (cited by Williamson, 1998) or after repeated exposure and selection on tomato cultivars with the Mi gene (Castagnone-Sereno et al., 1994). Such populations of M. javanica have been also found in Crete (Tzortzakakis et al., 1999) and the objective of this study was to characterize further populations from Greece.Populations were collected from vegetable crops from Preveza, Epirus (10 greenhouses) and Kyparissia, Peloponissos (one outdoor site) on mainland Greece and used to establish cultures on potted tomatoes. Egg masses from these cultures were used to inoculate (six egg masses per plant) seedlings of either the susceptible tomato cv. ACE or the nematode resistant cvs Nikita and Alpado grown in pots. The plants were grown in a controlled environment with a 16 h photoperiod and a soil temperature of 24-26°C. They were watered and fertilized as required and roots were examined after 7 weeks. If a large number of egg masses were produced on the resistant tomato cultivars, the egg masses were inoculated onto another plant and the process repeated. Four populations from Preveza (Mj P1, Mj P2, Mj P3 and Mj P4), which sustained high reproduction rates on resistant tomato cultivars for four successive tests were selected for further study. Two populations from Crete (Mj C1 and Mi C1) that had been sent to the laboratory

A targeted survey of vegetable production areas in Crete, Greece, showed that the majority of infestations of rootknot nematodes (RKN) were Meloidogyne javanica. M. incognita appeared to be limited to areas growing pepper that is a host for M. incognita but not for M. javanica. Tests with resistant tomato carrying the Mi gene showed that the M. incognita and the majority of the M. javanica populations were avirulent, and that virulent nematodes could not be selected from them. However, three populations of M. javanica, including some previously identified, were virulent. An AFLP study of the DNA from 22 populations of M. javanica produced 264 scorable amplification products and gave a very high mean similarity (99.4%) between populations, indicating that both virulent and avirulent populations probably derived from the same founder population. Mi-resistant tomato and pepper appear to have considerable utility in the integrated management of RKN in Crete, provided care is taken to monitor the species and virulence or reproductive ability of the nematode populations. Die Variation bei Wurzelgallennematoden (Meloidogyne spp.) auf Kreta in Bezug auf ihre Bekampfung mit resistenten Tomaten und Paprika - Eine gezielte Untersuchung von Gemuseanbaugebieten auf Kreta Griechenland, ergab, dass die Mehrzahl der von Wurzelgallennematoden (RKN) befallenen Flachen mit Meloidogyne javanica verseucht war. M. incognita was offentsichtlich auf Gebiete des Paprikaanbaus beschrankt. Paprika ist ein Wirt fur M. incognita aber nicht fur M. javanica . Versuche mit resistenten Tomaten, die das Mi-Gen besassen, zeigten, dass M. incognita und die Mehrzahl der Populationen von M. javanica avirulent waren, und dass aus ihnen keine virulenten Nematoden selektiert werden konnten. Drei Populationen von M. javanica, darunter schon einige schon vorher identifizierte, waren virulent. Eine AFLP-Untersuchung der DNA von 22 Populationen von M. javanica ergab 264 unterscheidbare Amplifikationsprodukte und zeigte eine hohe mittlere Ahnlichkeit (99,4%) zwischen den Populationen. Dies deutete daraufhin, das virulente and avirulente Populationen wahrscheinlich von der gleichen Grunderpopulation abstammten. Mi-resistente Tomaten und Paprika sind offensichtlich von betrachtlichen Nutzen bei der integrierten Bekampfung von RKN auf Kreta. Voraussetzung ist, dass die Arten und die Virulenz oder die Vermehrungsfahigkeit der Populationen sorgfalting festgestell werden.

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