Variability in infection and reproduction of Meloidogyne javanica on tomato rootstocks with the Mi resistance gene

The response of 10 commercial or experimental tomato rootstocks with the Mi resistance gene to an initial inoculum of a Mi-avirulent population of Meloidogyne javanica was determined in pot tests conducted in spring and summer. In a field test, the rootstocks were subjected to continuous exposure to high initial population densities (2050 ± 900 second-stage juveniles (J2) per 250 cm³ soil) of the nematode. The presence of the Mi locus in the resistant rootstocks and cultivars was confirmed using the PCR co-dominant markers REX-1 and Mi23. Nematode infectivity (egg masses) and reproduction (eggs g⁻¹ root) were highly variable in the spring tests. Rootstocks PG76, Gladiator and MKT-410 consistently responded as highly resistant, with nematode multiplication rate (Pf/Pi) < 1 and reproduction index (RI) < 10%, and they were as efficient as standard resistant tomato cultivars at nematode suppression. The relative resistance levels of rootstocks Brigeor, 42851, 43965, Big Power and He-Man varied depending on the susceptible standard used for reference or the duration of the test. Rootstocks Beaufort and Maxifort were susceptible to M. javanica (Pf/Pi > 50 and RI > 50%). Rootstocks PG76 and He-Man, and the resistant tomato cv. Caramba showed high levels of resistance in the test conducted in summer, whereas MKT-410 and 42851 and the resistant tomato cv. Monika were moderately resistant. In the field, seven rootstocks showed high levels of resistance and one (He-Man) showed an intermediate level, whereas Beaufort and Maxifort were susceptible.