Mapping cold tolerance quantitative trait loci (QTL) in a Citrus grandis x Poncirus trifoliata F(1) pseudo-testcross population using molecular markers and evaluation of homology with a related population map

The threat of damage from low temperatures is a great concern in the citrus growing regions of Florida. The related species, Poncirus trifoliata , has long been recognized as a desirable source for improved cold tolerance in citrus hybrids. However, the genetic component of this tolerance has not been determined, although it is known that cold tolerance in Poncirus is a quantitative trait inherited in a continuous manner in a segregating population. Two genetic linkage maps were produced for a Citrus grandis 'DPI 6-4' x Poncirus trifoliata 'Rubideaux' F1 pseudo-testcross population using molecular markers. The map for the Citrus parent is the first map based solely upon markers derived from Citrus and not mixed with markers from Poncirus. Random amplified polymorphic DNA (RAPD) markers proved to be efficient for mapping in this population and several quantitative trait loci associated with tolerance to cold were identified.;In addition, sequence-based PCR markers---including sequence-characterized amplified regions (SCAR), cleaved amplified polymorphic sequences (CAPS), and sequence-tagged sites (STS)---were designed for use in diverse citrus populations. A total of 26 polymorphic, sequence-based PCR markers were identified in the pseudo-testcross population with 24 mapped to 12 linkage groups on the parental maps. In a backcross population, 20/26 were polymorphic with 15 mapped to 7 linkage groups of a published map. Eleven of these markers were located on maps from both populations, allowing for the evaluation of homology between linkage groups on the different maps. The production of these markers was less technically demanding and was achieved in less time than the prevalent marker type used for homology studies between populations.