Identification of RAPD, SCAR, and RFLP markers tightly linked to nematode resistance genes introgressed from Arachis cardenasii into Arachis hypogaea.

Two dominant genes conditioning resistance to the root-knot nematode Meloidogyne arenaria were identified in a segregating F2 population derived from the cross of 4x (Arachis hypogaea x Arachis cardenasii)-GA 6 and PI 261942. Mae is proposed as the designation for the dominant gene restricting egg number and Mag is proposed as the designation for the dominant gene restricting galling. The high levels of resistance in GA 6 were introgressed from A. cardenasii and, therefore, a search to identify A. cardenasii specific RAPD markers that are tightly linked to these resistance genes was conducted utilizing bulked segregant analysis. One RAPD marker (Z3/265) was linked at 10 +/- 2.5 (SE) and 14 +/- 2.9 cM from Mag and Mae, respectively. The marker was mapped to linkage group 1 at 5 cM from Xuga.cr239 in the backcross map in an area where introgression from A. cardenasii had previously been reported. This fragment was cloned and used to generate a pair of primers that specifically amplified this locus (sequence characterized amplified region, SCAR) and as a RFLP probe. Their close linkage with the resistance genes will be useful in marker-based selection while transferring nematode resistance from introgression lines into elite breeding lines and cultivars. The Z3/265 marker associated with the genes Mae or Mag was not found in other highly resistant Arachis species (Arachis batizocoi or Arachis stenosperma), in progenies of interspecific crosses with A. cardenasii that were moderately resistant, or in the resistant A. hypogaea lines PI 259634 and PI 259572. These represent the first molecular markers linked with a resistant gene in peanut and the first report of two physiological responses to nematode attack associated with two genetic factors.