QTL analysis of Na+ and Cl- accumulation related traits in an intergenericBC1 progeny of Citrus and Poncirus under saline and nonsaline environments

The effects of salinization with 40 mM NaCl on Poncirus trifoliata (L.) Raf ., Citrus grandis (L.) Osb., their F-1, and a BC1 progeny population (C. gr andis x (F-1)) were investigated by means of Na+ and Cl- analyses and QTL ( quantitative trait loci) mapping. A total of 38 traits related to different tissue or whole-plant Na+ and (or) Cl- accumulation was analyzed in salini zed and nonsalinized BC1 progeny clones. The comparison of the three parent al types with the BC1 progeny under control and saline conditions showed th at the BC1 progeny plants segregated transgressively for many traits. First mapping analyses resulted in a total of 73 potential quantitative trait lo ci (PQTL) with LOD scores greater than or equal to 3.0 located on a previou sly generated linkage map. Fifty-three percent of the mapped PQTLs were for traits associated with salinity. The small progeny population size used ma de further analyses of these PQTLs necessary. By considering LOD scores, ma p locations, and correlation analyses of the traits, it was possible to ide ntify 17 regions of the citrus genome of interest: 8 of them may contain ge nuine QTLs of large effect and 9 regions are worthy of further study. Corre lation analyses and locations of PQTLs indicated that many traits were cont rolled by fewer genes than the actual number of QTLs mapped for them. For e xample, 21 PQTLs mapped for Na+ accumulation and Cl-/Na+ ratios were locate d in a cluster at the beginning of one linkage group (LG), while 10 PQTLs m apped for Cl- accumulation and Cl-/Na+ ratios were located in a cluster at the beginning of another LG. This is the first step in identifying QTLs tha t have a major impact on salt tolerance and (or) mineral accumulation in ci trus.