SALT TOLERANCE IN LYCOPERSICON SPECIES .6. GENOTYPE-BY-SALINITY INTERACTION IN QUANTITATIVE TRAIT LOCI DETECTION - CONSTITUTIVE AND RESPONSE QTLS

A study of genotype-by-salinity interaction was carried out to compare the behavior of quantitative trait loci (QTLs) in two F-2 populations derived from crosses between the cherry tomato, Lycopersicon esculent um Mill. var. cerasiforme, and two wild relatives Lycopersicon pimpine llifolium (Jusl.) Mill. and Lycopersicon chesmannii f. minor (Hook. f. ) Mull., grown at two environmental conditions (optimum and high salin ity). QTLs for earliness and fruit yield could be classified into four groups: ''response-sensitive'', those detected only under control con ditions or whose contribution significantly decreased in salinity; ''r esponse-tolerant'', detected only in salinity or in which the directio n of their additive effects changed; ''constitutive'', detected in bot h growing conditions; and ''altered'' QTLs, those where the degree of dominance changed according to the presence or absence of salt. Epista tic interactions were also influenced by the salt treatment. This diff erential allele effect at some (non-constitutive) QTLs induced by salt stress will make selection under an ''optimum environment'' unfruitfu l for the ''response-tolerant'' QTLs. Similarly, selection under salin ity will ignore ''response-sensitive'' QTLs. Given that salinity is hi ghly variable in the field, marker-assisted selection should take into account not only the ''response-tolerant'' but also the ''response-se nsitive'' QTLs although there might be cases where selection in some Q TLs for both conditions is not feasible. Comparing both populations, v ery few QTLs showed the same behavior.