Comparative histopathology of virulent and avirulent Meloidogyne javanica populations on susceptible and resistant tomato plants

The <i>Mi-</i>1.2 gene confers resistance to a wide range of <i>Meloidogyne</i> species, being the most important resistance factor employed in tomato breeding so far. However, many aspects related to the interaction of <i>Mi-</i>1.2-carrying tomato cultivars and virulent/avirulent <i>Meloidogyne</i> populations have not yet been clarified. Herein, comparative histopathological analyses were carried after inoculation of the homozygous (<i>Mi</i>-1.2/<i>Mi</i>-1.2) tomato rootstock 'Guardião' and the susceptible cultivar 'Santa Clara' (<i>mi</i>-1.2/<i>mi</i>-1.2) with virulent and avirulent populations of <i>M. javanica.</i> In the susceptible control, it was possible to visualize second stage juveniles (J2) of avirulent population and feeding sites from 2 to 30 days after infection (DAI) with females reaching maturity at 24-34 DAI. In the resistant rootstock, the <i>Mi-</i>1.2 gene-mediated resistance was related mainly to early defense responses (pre-infection and hypersensitive reaction), which led to an immunity-like phenotype that completely prevented the reproduction of the avirulent <i>Meloidogyne</i> population. On the other hand, J2s of the virulent <i>M. javanica</i> population were able to penetrate roots much more than the avirulent population, migrated and developed normally, showing intense and similar pattern of penetration from 4 to 34 DAI in the root tissues of both resistant and susceptible tomato genotypes. The total numbers of J2, J3, J4, and females counted in 'Santa Clara' for the virulent population of <i>M. javanica</i> were higher than in 'Guardião'.