Construction of citrus genome maps with AFLP markers (Molecular markers)

The Amplified Fragment Length Polymorphism (AFLP) marker system was used to construct a total citrus genome map based on an intergeneric backcross population of Citrus grandis (‘Thong Dee’) X USDA 17-40 (an F1 hybrid of C. grandis x Poncirus trifoliata). The map contains 337 DNA markers and a virus resistance gene (Ctv), and it was calculated by the JoinMap linkage analysis program. The map covers 858.6 cM of the citrus genome with 11 linkage groups, and an increased marker density of 2.5 cM/interval. A comparative analysis was conducted with the map based on AFLPs and one based on RAPD (random amplified polymorphic DNA) markers. Two maps were integrated, to generate a composite high-density citrus map with 509 markers of various types, covering a genetic distance of 1026.4 cM. The map density was compacted to 2.0 cM/interval. Map synteny analysis revealed genomic region rearrangements between major linkage groups of these two maps. Fifteen salt tolerance-related and 6 growth-related traits were selected for QTL analysis with MapQTL (JoinMap version) program. There were 36 putative QTLs found in association with growth-related traits, and 50 putative QTLs for salt tolerance-related traits. The possible genuine QTLs for those traits were analyzed further.; Marker-assisted selection was used to construct a localized genetic map for the Ctv gene region with AFLP markers. A subset of recombinants for Ctv-linked markers from a backcross population of Citrus and Poncirus were selected and subjected to CTV resistance phenotyping. Putative Ctv-linked AFLP markers were mapped, and the marker density in the Ctv region was increased. A consensus map was constructed based on three different mapping sources, which presented integrated map information of Ctv and a citrus nematode resistance gene region. These markers, along with those for salt tolerance, could be useful for marker-assisted selection in citrus rootstock breeding programs.