mon parents) and closely related species. Therefore, if statistical limitations are overcome, it will benefit comparative genomics and it will be a valuable tool to complement information obtained from vertical integration. The integration of QTL analyses of salt tolerance in tomato using wild relatives as donors of salt tolerance has been useful to judge between breeding strategies. Their utilization in rootstock breeding programs seems the most efficient one because most "good-rootstock" QTL alleles come from the wild species. Association mapping methods can be used to validate QTLs by testing the effects of linked markers or candidate genes within a large set of genotypes such as germplasm accessions or cultivated accessions. These or other methods of cross validation of QTL mapping results (particularly, allele effects) are absolutely necessary to ensure the success of marker-assisted selection.

Instead of inferring MAS schemes in breeding populations from QTL results in experimental (bi-parental) populations, the development of QTL mapping methods for multiparental populations is envisaged as a better alternative because it would allow to link QTL analysis and MAS in tandem through generations in the breeding program itself.

Acknowledgements This work was supported in part by a grant from MCI (RTA04-075-C2 and RTA2006-0009-00-00). Authors thank Dr. Alfredo Miguel from IVIA and Dr. Carlos Biaxial from Foundation "Ruralcaja" of Valencia for the grafting, culture and evaluation of the Solanum RIL populations as rootstock under optimal growing conditions.

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