Development and characterization of a codominant marker linked to root-knot nematode resistance, and its application to peach rootstock breeding

The presence of a codominant AFLP marker, EAA/MCAT10, correlates with the p rimary source of resistance to root-knot nematodes (Meloidogyme incognita a nd hi. javanica) in rootstock cultivars of peach [Prunus persica (L.) Batsc h]. Two allelic DNA fragments of this AFLP marker were cloned, sequenced an d converted to sequence tagged sites (STS). Four nucleotide differences (i. e. one addition and three substitutions) were observed between the two clon es. Furthermore, there was a diagnostic Sau3 AT cleavage site (GATC) in the large fragment that was absent from the small fragment (GTTC at this site) . The applicability of this STS marker system to peach germplasm improvemen t was evaluated: genomic DNAs of cross parents (i.e. 'Lovell' and 'Nemared' ), four F-1 hybrids (K62-67, K62-68, P101-40 and P101-41) and two F-2 popul ations (from K62-68 and P101-41), as well as DNA from a test panel of IX ro otstock cultivars or selections, were PCR-amplified with the Mij3F/Mij1R pr imer pair and then digested with Sau3 AI, The banding patterns showed that the EAA/MCAT10 STS markers can clearly distinguish the three genotypes - ho mozygous resistant, heterozygous resistant and homozygous susceptible - in the 'Lovell' x 'Nemared' cross. In addition, results from the rootstock sur vey were consistent with each rootstock's phenotypic response to nematode i nfection, except for 'Okinawa', 'Flordaguard' and 'Yunnan' where root-knot resistance may have arisen independently. Therefore, the EAA/MCAT10 STS mar kers will be a useful tool to initiate marker assisted selection studies in peach rootstock breeding for root-knot nematode resistance.