Genetic analysis of salt tolerance in a progeny derived from the citrus rootstocks Cleopatra mandarin and trifoliate orange

A total of 60 traits that could be related to salt tolerance were genetically analyzed using nucellar plants as repetitions of apomictic hybrids in a reference population derived from two common citrus rootstocks, Cleopatra mandarin (salt tolerant) and trifoliate orange (salt sensitive), in two experiments differing in duration (1 versus 3 years) [NaCl] (30 versus 25 mM) and environmental control (greenhouse versus screenhouse). In both experiments, the trifoliate parent always showed less aerial vegetative growth than Cleopatra, and under salinity, the trifoliate parent showed higher Na+ and Cl− leaf concentrations than the salt-tolerant parent. Salinity affected the relationships among traits, particularly those involving leaf water potential; leaf concentrations of Cl−, K+, B and Fe; and root [Na+]. Most traits showed heritabilities below 0.6, and their quantitative trait locus (QTL) analyses were carried out using three mapping procedures to obtain complementary genetic information on trait inheritance. A total of 98 QTLs were detected by interval mapping and multiple QTL mapping procedures. Fresh and dried weights of the leaf, studied in both experiments, showed common QTLs, remarking their repeatability. A cluster of QTLs governing plant vigour and leaf boron concentration pointed a genomic region in linkage group 3 as the most relevant one to improve salt tolerance using the Cleopatra parent as donor. Besides, a QTL genotype in linkage group 7, associated with the smallest leaf water potential and defoliation index under salinity, corresponded to the highest leaf [Na+] and the largest leaf area, suggesting the presence of a putative tissue salt tolerance QTL.