Abstract
With the banning of most chemical nematicides, the control of root-knot nematodes (RKNs) in vegetable crops is now based essentially on the deployment of single, major resistance genes (R-genes). However, these genes are rare and their efficacy is threatened by the capacity of RKNs to adapt. In pepper, several dominant R-genes are effective against RKNs, and their efficacy and durability have been shown to be greater in a partially resistant genetic background. However, the genetic determinants of this partial resistance were unknown. Here, a quantitative trait loci (QTL) analysis was performed on the F2:3 population from the cross between Yolo Wonder, an accession considered partially resistant or resistant, depending on the RKN species, and Doux Long des Landes, a susceptible cultivar. A genetic linkage map was constructed from 130 F2 individuals, and the 130 F3 families were tested for resistance to the three main RKN species, Meloidogyne incognita, M. arenaria, and M. javanica. For the first time in the pepper-RKN pathosystem, four major QTLs were identified and mapped to two clusters. The cluster on chromosome P1 includes three tightly linked QTLs with specific effects against individual RKN species. The fourth QTL, providing specific resistance to M. javanica, mapped to pepper chromosome P9, which is known to carry multiple NBS–LRR repeats, together with major R-genes for resistance to nematodes and other pathogens. The newly discovered cluster on chromosome P1 has a broad spectrum of action with major additive effects on resistance. These data highlight the role of host QTLs involved in plant-RKN interactions and provide innovative potential for the breeding of new pepper cultivars or rootstocks combining quantitative resistance and major R-genes, to increase both the efficacy and durability of RKN control by resistance genes.
Highlights
Root-knot nematodes (RKNs), Meloidogyne spp., are major plant pathogens worldwide
The pepper genetic map constructed in this study with 130 F2 plants from the cross between YW and DLL comprised 12 linkage group (LG), consistent with the known number of chromosomes in pepper, and it covered a total length of 1436 cM, consistent with previous maps for pepper (Lefebvre et al, 2002; Paran et al, 2004; Wu et al, 2009)
As only a few of the previously used markers proved to be polymorphic between the parental lines YW and DLL, new single-nucleotide polymorphism (SNP) had to be developed to complete the map
Summary
Root-knot nematodes (RKNs), Meloidogyne spp., are major plant pathogens worldwide. These extremely polyphagous endoparasites can infest more than 5,500 plant species, including many field and greenhouse crops (Goodey et al, 1965). Several management strategies have been developed, to prevent the breakdown of resistance by pathogens Most of these approaches are based on spatiotemporal management of the deployment of R-genes: (i) alternation of different R-genes in the crop rotation, (ii) use of mixtures of cultivars with different R-genes, or (iii) pyramiding, the introduction of several R-genes into the same cultivar (Kiyosawa, 1982; Mundt, 2002; Pink, 2002). The use of such strategies requires several R-genes to be available, with no emergence of cross-virulent pathogens. Recent experimental studies have shown that the pyramiding of R-genes is the best method for promoting effective, durable RKN resistance in pepper (Djian-Caporalino et al, 2014)
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