Phenotypic Characterization and Molecular Mapping of Recessive Resistance To Meloidogyne Javanica in Cucumber, Cucumis Sativus

Abstract The Javanese root-knot nematode (JRKN, Meloidogyne javanica) is a serious pest of cucumber (Cucumis sativus) grown in tropical and subtropical regions. The recessive mj resistance gene first identified in the wild cucumber (C. sativus var. hardwickii), is the only known source of resistance to JRKN within the C. sativus gene pool. Despite its potential utility as a nematode management tool, the mj trait has yet to be fully characterized or widely incorporated into commercial cucumber lines. In this study, we mapped the mj resistance locus to a 148-kb interval on cucumber chromosome 1 by phenotyping a recombinant inbred line (RIL) and targeted backcross populations. The genomic interval is predicted to contain 36 candidate genes, including several known to be directly related to plant defense against pathogens. We also conducted histological comparisons of nematode development in mj resistant and susceptible lines, providing evidence that the mechanism of action for this gene may be different from that of known RKN resistance genes. These results provide a set of tightly linked markers that can assist breeding programs seeking to incorporate mj resistance into new cucumber varieties. The candidate genes will also provide a starting point for further research into the mechanisms of action that underlay the mj-regulated JRKN resistance.