Assessment of Prunus Rootstock Accessions Using Chloroplast and Nuclear Microsatellites

A rootstock collection of Prunus species and hybrids is maintained at the U.S. Department of Agriculture stone fruit breeding program at Byron, GA. We genotyped 66 Prunus rootstock accessions and clones using chloroplast and nuclear microsatellites in this study. Chloroplast microsatellites revealed that the accessions belong to four previously defined maternal lineage groups (MLG-1 to -4) and five new ones (MLG-9 to -13). MLG-1 and -2 share the same chloroplast alleles of ‘Chinese Cling’ peach (Prunus persica) derived scions and American scions and rootstocks related to early European introductions, respectively. MLG-3 included ‘Guardian’ rootstock and its descendants. MLG-4 had a single genotype, ‘Okinawa’, that is the maternal parent of ‘Flordaking’. MLG-9 and MLG-11 to -13 included hybrids with different plums (Prunus salicina, Prunus cerasifera, Prunus tomentosa, or Prunus angustifolia) in their maternal parentage. MLG-10 included hybrids from almond (Prunus. dulcis) in the maternal parentage. The neighbor-joining phylogenetic tree based on nuclear microsatellite genotyping data showed several clusters. Cluster I included only one scion cultivar Elberta from MLG-1. Clusters II, III, and V contained peach accessions mostly in MLG-2. Clusters IV and VI included accessions mostly in MLG-3. Cluster VII included most accessions of plum-peach hybrid origin and those found within MLG-13. Cluster VIII was found to be mixed with different plum-peach hybrids and hybrids from other Prunus species, most of which were found in MLG-10, -11, and -12. Most accessions in Cluster IX were related to plums in MLG-11 and a few accessions in MLG-9.