Importance of the genetic background for sustainable resistance: experimental evidence for a major resistance gene to nematodes

Root-knot nematodes, Meloidogyne spp., are extremely polyphagous plant parasites worldwide. Since the use of most chemical nematicides is being prohibited, genetic resistance is an efficient alternative way ta protect crops against these pests. However, resistance genes (R-genes) are limited and nematode populations are able ta overcome them with time. Good management of these valuable resources is thus a key point of R-gene durability. ln pepper, Me3 is a dominant major resistance gene, currently used in breeding programs, that control M. arenario, M. incognito and M. javanica, the three main root-knot nematodes species. ln this study, it was introgressed in either a susceptible or a partially resistant genetic background in either homozygous or heterozygous allelic status. Confronting these genotypes with a high inoculation pressure of an avirulent M. incognito isolate or a Me3 virulent laboratory-selected population (obtained by successive re-inoculation on a Me3 R-pepper line) demonstrated i) that the genetic background plays an important raie, Me3 being overcome more easily in a susceptible genetic background than in a partially resistant one, ii) that the allelic status has no effect. These results are in good agreement with concepts recently developed from the analysis of very different plant-pathogen interactions: pepper-virus (Palloix et al., 2009) or rapeseed-Leptosphaeria (Brun et al., 2012). Experiments are now underway ta detect and localise genes or loci providing partial resistance (QTLs = Quantitative Trait Loci) ta root-knot nematodes explaining the differences observed between susceptible and partially resistant genetic backgrounds, and ta determine the effectiveness of their « protective » raie on the major R-genes. Ali these results are of main importance for the creation of new varieties by breeders who have to take into account the plant material used and the resistance gene they want ta introgress