SALT TOLERANCE IN LYCOPERSICON SPECIES .4. EFFICIENCY OF MARKER-ASSISTED SELECTION FOR SALT TOLERANCE IMPROVEMENT

The usefulness of,marker-assisted selection (MAS) to develop salt-tole rant breeding lines from a F-2 derived from L. esculentum x L. pimpine llifolium has been studied. Interval mapping methodology of quantitati ve trait locus (QTL) analysis was used to locate more precisely previo usly detected salt tolerance QTLs. A new QTL for total fruit weight un der salinity (TW) near TG24 was detected. Most of the detected QTLs [3 for TW, 5 for fruit number, (FN) and 4 for fruit weight (FW)] had low R(2) values, except the FW QTL in the TG180-TG48 interval, which expl ains 36.6% of the total variance. Dominant and overdominant effects we re detected at the QTLs for TW, whereas gene effects at the QTLs for F N and FW ranged from additive to partial dominance. Phenotypic selecti on of F-2 familes and marker-assisted selection of F-3 families were c arried out. Yield under salinity decreased in the F-2 generation. F-3 means were similar to those of the F-1 as a consequence of phentoypic selection. The most important selection response for every trait was o btained from the F-3 to F-4 where MAS was applied. While F-3 variation was mainly due to the within-family component, in the F-4 the FN and FW between-family component was larger than the within-family one, ind icating an efficient compartmentalization and fixation of QTLs into th e F-4 families. Comparison of the yield of these families under contro l versus saline conditions showed that fruit weight is a key trait to success in tomato salt-tolerance improvement using wild Lycopersicon g ermplasm. The QTLs we have detected under salinity seem to be also wor king under control conditions, although the interaction family x treat ment was significant for TW, thereby explaining the fact that the sele cted families responded differently to salinity.