Cloning and mapping of resistance gene homologues in melon

Four families of resistance gene homologues containing the nucleotide bindi ng site (NBS) motif were obtained in Cucumis melo using degenerate primers designed from two conserved regions of known disease resistance genes. The four homologues had high levels of amino acid identity to NBS-containing re sistance genes found in other species. Three of these homologues (MRGH4, MR GH21 and MRGH63) were placed in the genetic map of melon. The RFLP detected with MRGH21 was located on the distal part of Linkage Group 7. Homologues MRGH63 and MRGH4 detected RFLPs that mapped to Linkage Group 4. The map pos itions of these loci relative to those of resistance genes mapped in melon and the potential use of these loci in marker-assisted selection and map-ba sed cloning strategies is discussed. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.