Plant parasitic nematodes belonging to the genus Meloidogyne are the most economically harmful nematodes worldwide with the widest host range. In the seventies, commercial tobacco cultivars with the Rk1 gene, which imparts resistance to Meloidogyne incognita races 1 and 3 and Meloidogyne arenaria race 1, started to be released. This gene has an impact on giant cell formation and was recently characterized on chromosome 17. A second locus, with a different mechanism (referred to as Rk2), was identified in Zimbabwe in plants and determined to be partially resistant to M. javanica, and crossed with cultivated tobacco entries to improve agronomic traits, resulting in the breeding line RKT15-1-1. In the nineties, Rk2 was incorporated in commercial varieties together with Rk1 for increased efficiency, against M. javanica, and for M. arenaria.

Until now, the mechanism of Rk2 remains unclear and several hypotheses have been proposed: dominant, multiple factors or modifying genes related to the background. The difficulty of phenotyping is the main barrier for its characterization. It is not unusual to have galls even with tolerant plants in high pressure conditions. Moreover, the effect of Rk2 alone is less visible than Rk1 alone.

In this study, a population resulting from the cross of two Rk1 tobaccos, and segregating for Rk2, was used in different experimental conditions: F6 recombinant inbred lines were assessed in a nursery in southern Brazil during two crops, in the presence of M. arenaria and M. javanica. An F₂ population was rated in France, in an open field trial, under M. arenaria infestation. Both parents were submitted to re-sequencing experiments and 2,000 single nucleotide polymorphism (SNPs) markers were selected for a linkage mapping and qualitative trait locus (QTL) approach. Both populations were then characterized by SeqSNPs. The first results of this QTLs approach are presented here.