High-resolution genetic mapping of the pepper (Capsicum annuum L.) resistance loci Me-3 and Me-4 conferring heat-stable resistance to root-knot nematodes (Meloidogyne spp.)

The PM687 line of Capsicum annuum L. has a single dominant gene, Me-3, that confers heat-stable resistance to root-knot nematodes (RKN). Me-3 was mapp ed using doubled-haploid (DH) lines and F-2 progeny from a cross between th e susceptible cultivar 'Yolo Wonder' ('YW') and the highly resistant line ' PM687'. Bulked-segregant analysis with DNA pools, from susceptible or resis tant DH lines, was performed to identify RAPD and AFLP markers linked to Me -3. There was no polymorphism between bulks of ten DH lines using over 800 RADP primers (4,000 amplified fragments analysed). Using 512 AFLP primers ( 74,000 amplified fragments analysed), and bulked DNA templates from 20 resi stant and 20 susceptible plants, we identified eight repulsion-phase and fo ur coupling-phase markers linked to Me-3. Analysed in 103 DH progeny, they defined a 56.1-cM interval containing the target gene. The nearest were loc ated 0.5, 1.0, 1.5 and 3.0 centimorgans (cM) on both sides of the gene. Ana lysis of the F-2 progeny (162 plants) with the nearest coupling-phase marke r confirmed its close position. Another resistance gene to RKN, present in 'PM687' (Me-4), was shown to be linked to Me-3, 10 cM from it. In order to localize Me-3 and Me-4 on our reference intraspecific pepper linkage map, t wo AFLP markers were mapped. The Me-3 nearest marker was 10,1 cM from a RAP D marker named Q04_0.3 and 2.7 cM from a RFLP marker named CT135. We invest igated map-position orthologies between Me-3 and two other nematode resista nce genes, the tomato Mi-3 and the potato Gpa(2) genes, which mapped in the telomeric region of the short arm of the tomato and potato chromosome 12 ( or XII for potato).