Abstract
The root-knot nematode (RKN) Meloidogyne incognita severely reduces yields of pepper (Capsicum annuum) worldwide. A single dominant locus, Me7, conferring RKN resistance was previously mapped on the long arm of pepper chromosome P9. In the present study, the Me7 locus was fine mapped using an F2 population of 714 plants derived from a cross between the RKN-susceptible parent C. annuum ECW30R and the RKN-resistant parent C. annuum CM334. CM334 exhibits suppressed RKN juvenile movement, suppressed feeding site enlargement and significant reduction in gall formation compared with ECW30R. RKN resistance screening in the F2 population identified 558 resistant and 156 susceptible plants, which fit a 3:1 ratio confirming that this RKN resistance was controlled by a single dominant gene. Using the C. annuum CM334 reference genome and BAC library sequencing, fine mapping of Me7 markers was performed. The Me7 locus was delimited between two markers G21U3 and G43U3 covering a physical interval of approximately 394.7 kb on the CM334 chromosome P9. Nine markers co-segregated with the Me7 gene. A cluster of 25 putative nucleotide-binding site and leucine-rich repeat (NBS-LRR)-type disease resistance genes were predicted in the delimited Me7 region. We propose that RKN resistance in CM334 is mediated by one or more of these NBS-LRR class R genes. The Me7-linked markers identified here will facilitate marker-assisted selection (MAS) for RKN resistance in pepper breeding programs, as well as functional analysis of Me7 candidate genes in C. annuum.
Highlights
Root-knot nematodes (RKN; Meloidogyne spp.) are obligate phytopathogens causing significant economic losses in several crops including Solanaceae species (Eisenback and Triantaphyllou, 1991; Bernard et al, 2017)
At 10 dai, no cell necrosis was noticed in Early Calwonder 30R (ECW30R), whereas necrosis was observed in Criollo de Morelos 334 (CM334) cells, as a result of a hypersensitive response (HR) (Figure 1C), indicating that CM334 is highly resistant to M. incognita
At 10 dai, giant cell development was initiated in both lines, the stele cells were slightly narrower and denser with enlarged feeding sites in ECW30R compared to CM334 (Figure 1D; f–j)
Summary
Root-knot nematodes (RKN; Meloidogyne spp.) are obligate phytopathogens causing significant economic losses in several crops including Solanaceae species (Eisenback and Triantaphyllou, 1991; Bernard et al, 2017). Meloidogyne arenaria, M. incognita, M. hapla, and M. javanica, Pepper Me7 Locus Mapping are widely distributed with diverse host ranges and cause considerable yield losses in many crops (Jones et al, 2013; Noling, 2014; Wu et al, 2018). Strategies to mitigate the RKN threat include biological and chemical control measures as well as the use of resistant cultivars/rootstocks. Since nematoderesistant cultivars provide an efficient and environmentally safe alternative to chemical measures, much effort has been devoted to identifying host resistance against RKN in cultivated or in wild species (Taylor and Sasser, 1978; Pegard et al, 2005)
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