Salt tolerance in Lycopersicon species .6. Genotype-by-salinity interaction in quantitative trait loci detection: constitutive and response QTLs
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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 esculentum Mill. var. cerasiforme, and two wild relatives Lycopersicon pimpinellifolium (Jusl.) Mill. and Lycopersicon chesmannii f. minor (Hook. f.) Mull., grown at two environmental conditions (optimum and high salinity). QTLs for earliness and fruit yield could be classified into four groups: ''response-sensitive'', those detected only under control conditions or whose contribution significantly decreased in salinity; ''response-tolerant'', detected only in salinity or in which the direction of their additive effects changed; ''constitutive'', detected in both growing conditions; and ''altered'' QTLs, those where the degree of dominance changed according to the presence or absence of salt. Epistatic interactions were also influenced by the salt treatment. This differential allele effect at some (non-constitutive) QTLs induced by salt stress will make selection under an ''optimum environment'' unfruitful for the ''response-tolerant'' QTLs. Similarly, selection under salinity will ignore ''response-sensitive'' QTLs. Given that salinity is highly variable in the field, marker-assisted selection should take into account not only the ''response-tolerant'' but also the ''response-sensitive'' QTLs although there might be cases where selection in some QTLs for both conditions is not feasible. Comparing both populations, very few QTLs showed the same behavior.