Root-knot nematode (Meloidogyne spp.) Me resistance genes in pepper (Capsicum annuum L.) are clustered on the P9 chromosome

Abstract

The root-knot nematode (Meloidogyne spp.) is a major plant pathogen, affecting several solanaceous crops worldwide. In Capsicum annuum, resistance to this pathogen is controlled by several independent dominant genes--the Me genes. Six Me genes have previously been shown to be stable at high temperature in three highly resistant and genetically distant accessions: PI 322719, PI 201234, and CM334 (Criollo de Morelos 334). Some genes (Me4, Mech1, and Mech2) are specific to certain Meloidogyne species or populations, whereas others (Me1, Me3, and Me7) are effective against a wide range of Meloidogyne species, including M. arenaria, M. javanica, and M. incognita, the most common species in Mediterranean and tropical areas. These genes direct different response patterns in root cells depending on the pepper line and nematode species. Allelism tests and fine mapping using the BSA-AFLP approach showed these genes to be different but linked, with a recombination frequency of 0.02-0.18. Three of the PCR-based markers identified in several genetic backgrounds were common to the six Me genes. Comparative mapping with CarthaGene software indicated that these six genes clustered in a single genomic region within a 28 cM interval. Four markers were used to anchor this cluster on the P9 chromosome on an intraspecific reference map for peppers. Other disease resistance factors have earlier been mapped in the vicinity of this cluster. This genomic area is colinear to chromosome T12 of tomato and chromosome XII of potato. Four other nematode resistance genes have earlier been identified in this area, suggesting that these nematode resistance genes are located in orthologous genomic regions in Solanaceae.

Development of a SNP-based CAPS assay for the Me1 gene conferring resistance to root knot nematode in pepper

“…Firstly, SSCP-B54 was reported to be closely linked to Me3-Me4 and Me7-Mech1 and not Me1. Secondly, the Me cluster in pepper is large and estimated to span some 28 cM (Djian-Caporalino et al 2007). In contrast to the situation with SSCP-B54, SCAR-CD mapped in close proximity to Me1 in our population (1.9 cM away).…”

“…PM217 (resistant inbred derived from PI 201234 and carrying Me1). However, the Me1 specific marker (SCAR-CD) developed by Djian-Caporalino et al (2007) was linked to the gene in our population; but, as a dominant marker, it is not ideal for marker-assisted selection. To meet this need, we developed a tightlylinked codominant marker that would help us identify both homozygous and heterozygous resistant individuals in our PM217-derived pepper population.…”

“…Genotyping the F 2 population with chromosome 9 markers DNA was isolated from frozen leaf tissue (200 mg/ sample) of the parental genotypes and 200 F 2 individuals using a CTAB method (Doyle and Doyle 1990). DNA from 100 F 2 individuals inoculated with the M. incognita race 2 isolate D5 was used to amplify the Me-specific markers SSCP-B54, SSCP-B322, SCAR-B94, SCAR-CD and CAPS-F4R4 according to Djian-Caporalino et al (2007). Chromosome 9 SSR markers HPMS 1-3, HPMS 1-117, HPMS 2-41, HPMSE 102 (Lee et al 2004), GPMS171 and GPMS172 (Ben-Chaim et al 2006;Yi et al 2006) were also tested.…”

“…We tested the five Me-specific markers (Djian-Caporalino et al 2007) in 100 F 2 individuals inoculated with race 2 isolate D5. SSCP-B322, SCAR-B94 and CAPS-F4R4 were not polymorphic in our population and therefore could not be mapped.…”

“…In the process of mapping the Me genes, Djian-Caporalino et al (2007) developed several Me-specific markers. While these PCR-based markers reportedly showed promise in the breeding lines tested by Djian-Caporalino et al (2007), we found that the majority of these markers were either not polymorphic or did not co-segregate with nematode resistance in an F 2 population generated from the cross C. annuum cv. AZN-1 (susceptible line from Turkey) 9 C. annuum cv.…”