Identification and validation of QTLs for salt tolerance during vegetativegrowth in tomato by selective genotyping

The purpose of this study was to identify quantitative trait loci (QTLs) fo r salt tolerance (ST) during vegetative growth (VG) in tomato by distributi onal extreme analysis and compare them with the QTLs previously identified for this trait. A BC1 population (N = 792) of a cross between a moderately salt-sensitive Lycopersicon esculentum Mill. breeding line (NC84173, matern al and recurrent parent) and a salt-tolerant L. pimpinellifolium (Jusl.) Mi ll. accession (LA722) was evaluated for ST in solution cultures containing 700 mM NaCl + 70 mM CaCl2 (electrical conductivity, EC approximately 64 dS/ m and psi (w) approximate to -35.2 bars). Thirty-seven BC1 plants (4.7% of the total) that exhibited the highest ST were selected (referred to as the selected population), grown to maturity in greenhouse pots and self-pollina ted to produce BC1S1 progeny seeds. The 37 selected BC1S1 progeny families were evaluated for ST and their average performance was compared with that of the parental BC1 population before selection. A realized heritability of 0.50 was obtained for ST in this population. The 37 selected BC1 plants we re subjected to restriction fragment length polymorphism (RFLP) analysis us ing 115 markers, and marker allele frequencies were determined. Allele freq uencies for the same markers were also determined in an unselected BC1 popu lation (N = 119) of the same cross. A trait-based marker analysis (TBA), wh ich measures differences in marker allele frequencies between selected and unselected populations, was used to identify marker-linked QTLs. Five genom ic regions were detected on chromosomes 1, 3, 5, 6, and 11 bearing signific ant QTLs for ST. Except for the QTL on chromosome 3, all QTLs had positive alleles contributed from the salt tolerant parent LA722. Of the five QTLs, three (those on chromosomes 1, 3, and 5) were previously identified for thi s trait in another study, and thus were validated here. Only one of the maj or QTLs that was identified in our previous study was not detected here. Th is high level of conformity between the results of the two studies indicate s the genuine nature of the identified QTLs and their potential usefulness for ST breeding using marker-assisted selection (MAS). A few BC1S1 families were identified with most or all of the QTLs and with a ST comparable to t hat of LA722. These families should be useful for the development of salt t olerant tomato lines via MAS.