Molecular genetic mapping of the plum pox virus resistance genes in apricot

Plum pox virus (PPV) is a devastating disease of Prunus trees such as apricot, peach, plum, nectarine and cherry. It is the most economically important disease of fruit crops in Europe and as of 1999 has found its way into the United States. Development of molecular genetic markers associated with disease resistance in Prunus species could prove to be a valuable tool in combating disease caused by PPV. In order to do this, a molecular genetic approach has been initiated to map putative resistance regions associated with resistance in apricot. Four dominant AFLP markers segregating with resistance to PPV have been previously mapped in the crosses 'Stark Early Orange' (resistant) × 'LE-3218' (a susceptible selection) and 'Vestar' (susceptible) x 'LE-3246' (a resistant selection). The markers EAA/MCAG, EAG/MCAT, EAT/MCCT, and ETC/MCCT are located 4.5, 4.5, 13.3, and 16.4 cM respectively from the putative resistance gene. In order to further characterize this region, each marker was cloned, sequenced and hybridized to an apricot BAC library. Eleven apricot BACs were positively identified as containing a specific AFLP marker fragment. Based on Hind III digestion patterns of these BACs, 6 of the 11 BACs were chosen for sub-cloning and hybridized to the SSR (simple sequence repeats) oligonucleotide probes. Sub-clones that hybridized to the oligonucleotide probes were sequenced in order to develop SSRs in this region. Eight SSRs identified are currently being investigated to determine their potential for mapping and screening in other crosses. Due to the co-dominant nature of SSRs and their high genetic transportability, development of SSRs linked to resistance to PPV in apricot could allow the plant breeder to use MAS (marker assisted selection) to screen resistant cultivars in apricot and potentially in other Prunus species.