Mapping quantitative trait loci for salt tolerance and cold tolerance in Citrus grandis (L.) Osb. x Poncirus trifoliata (L.) Raf. hybrid populations

Quantitative trait loci (QTLs) influenced by salinization have been identified in a previously mapped BC1 progeny population of (C. grandis) x (C. grandis x P. trifoliata). Each progeny plant was vegetatively propagated to provide multiple control and salinized clones. Traits assayed included growth and dry weight, and Na+ and Cl- accumulation in individual plant tissues and in whole plants. Important genomic regions were identified based on lod scores, map positions of various traits, and correlation coefficients between traits. QTLs apparently important in freezing tolerance were identified through an analysis of a large segregating F-1 population of C. grandis x P. trifoliata. Plants were frozen at two temperatures to identify the most freeze-susceptible and freeze-tolerant individuals after acclimation. Assays were based on freeze damage and subsequent regrowth. DNA of selected individuals was used to create freeze-tolerant and freeze-susceptible bulks for use in bulked segregant analysis. Results from this analysis were compared with those from interval mapping using random amplified polymorphic DNA (RAPD) markers. Co-dominant markers are now being created so that the maps of these two populations can be aligned to determine whether regions of the genome important in salinity tolerance are also important in cold tolerance.