Resistance screening in progenies of carrot wild relatives × carrot breeding lines to the northern root-knot nematode (Meloidogyne hapla) and histological characterization of plant-nematode interaction

In Central and Northern Europe, the northern root-knot nematode Meloidogyne hapla is one of the most important pests in carrot production. Extensive galling, forking of the taproot and enhanced lateral root formation can completely prevent commercial usage of the carrots. Currently, no M. hapla resistant carrot cultivars are available. The study presents the evaluation of carrot wild relatives as well as progenies of wild relatives × carrot breeding lines in a climatic chamber test for resistance to M. hapla. Individual plants were cultivated in sand-filled plastic boxes for four weeks followed by inoculation with 400 s-stage juveniles (J2) of M. hapla per plant. After incubation for nine to ten weeks the plant roots were washed and stained with Cochenille A. Galls and egg masses were counted visually. Most of the tested wild relatives and a number of individual plants of wild relatives × carrot breeding lines showed a reduced number of galls and egg masses in comparison to the susceptible carrot 'Rotin'. Altogether 107 plants, completely without galls and egg masses, were selected for seed production. These progenies are available for future genetic studies. Histological slices of root tissue with galls and egg masses of different stages were prepared to investigate the plant-nematode interaction during pathogenesis. The non-destructive resistance screening approach, combined with histological analyses, represents the methodical basis for further breeding activities.