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SummaryDespite their unsuitability for agricultural production, the wild relatives of crop species represent a largely untapped resource of novel QTLs potentially useful for crop plant improvement. In this regard, previous introgression studies, involving several different wild tomato species, have shown that the long arm of chromosome 4 contains QTLs for many horticulturally important traits including soluble solids content, fruit shape, lycopene content and biochemical composition. However, these earlier studies were unable to determine how many genes control these traits and whether genes affecting the same character from different wild species are allelic or not. In an effort to shed light on these issues, we have constructed a series of lines containing small, overlapping introgressions for portions of the long arm of chromosome 4 from L. peruvianum and L. hirsutum and tested these lines in replicated field trials. The results provide evidence for multiple, non-allelic loci controlling soluble solids and fruit weight. They also show that the loci controlling some traits (e.g. fruit shape, fruit weight, epidermal reticulation) co-localize to the same portions of chromosome 4, a result that may be attributed to pleiotropy and/or gene dense areas with lower than average recombination. The implications of these finding for molecular breeding and utilization of exotic germplasm are discussed.

Abstract:The near-isogenic line (NIL) TA1150 contains a 56-cM introgression from Lycopersicon chmielewskii chromosome 1 and has several interesting phenotypic characteristics including fruit with orange color, high levels of soluble solids, thick pericarp, small stem scars, and good firmness. A set of overlapping recombinant lines (subNILs) was developed and field tested to fine map the quantitative trait loci (QTL) controlling these traits. The results indicated that the solids, pericarp thickness, and firmness QTL are distinct from the color locus. Several of the QTL mapped in this study, including the soluble-solids QTL, probably correspond to QTL mapped in other wild species of tomato. However, analysis of a set of TA523 subNILs containing complementary introgressions from Lycopesicon hirsutum chromosome 1 suggests that this wild species may contain a different locus for improved soluble solids. Thus, it might be possible to combine the L. chmielewskii and L. hirsutum alleles for these loci in a single line with the potential for extremely highly soluble solids. The TA1150 subNIL TA1688 contains the smallest introgression of the solids locus (approximately 19 cM), as well as the pericarp thickness and firmness QTL, with a yield that was equivalent to two of the three control lines. Isolation of recombinant subNILs from TA1688 should break the linkage between orange color and high solids and provide a small introgressed segment for marker-assisted breeding and genetic improvement of processing tomato.Key words: tomato, QTL, soluble solids, Brix, colour.Résumé : La lignée quasi-isogénique (NIL) TA1150 contient un segment de 56 cM introgressé à partir du chromosome 1 du Lycopersicon chmielewskii et elle présente de nombreuses caractéristiques phénotypiques intéressantes dont des fruits orange, une forte teneur en solides solubles, un péricarpe épais, de petites cicatrices axillaires et une bonne fermeté. Des lignées recombinantes chevauchantes (subNIL) ont été développées et évaluées au champ pour réaliser une cartographie fine des locus à caractère quantitatif (QTL) contrôlant ces caractéristiques. Les résultats indiquent que les QTL pour les solides, l'épaisseur du péricarpe et la fermeté sont différents de ceux contrôlant la couleur. Plusieurs des QTL qui ont été localisés au cours de cette étude, dont les QTL pour les solides solubles, correspondent vraisemblablement à des QTL identifiés chez d'autres espèces de tomate sauvages. Cependant, une analyse de subNIL du TA523 qui comprend des introgressions supplémentaires du chromosome 1 du Lycopesicon hirsutum suggère que cette espèce pourrait contenir un locus différent pour ce qui est de la teneur en solides solubles. Ainsi, il pourrait s'avérer possible de combiner les allèles du L. chmielewskii et du L. hirsutum pour ces deux locus chez une seule lignée, laquelle pré-senterait potentiellement une très forte teneur en solides solubles. La subNIL TA1688 de la lignée TA1150 contient la plus petite introgression du locus des solides solubles (environ 19 cM) de ...