Inheritance and genetic mapping of fruit sucrose accumulation in <i>Lycopersicon chmielewskii</i>

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<jats:p>Fruit of the domestic tomato (<jats:italic>Lycopersicon esculentum</jats:italic> Mill.) accumulate soluble sugars primarily in the form of the hexoses, glucose and fructose. In contrast, the predominant sugar in fruit of the wild tomato relative, <jats:italic>L. chmielewskii</jats:italic>, is sucrose. In the present study, the inheritance and linkage relations of sucrose accumulation were examined in interspecific <jats:italic>L. esculentum</jats:italic> x <jats:italic>L. chmielewskii</jats:italic> populations. In backcrosses to either the wild or domestic tomato, segregation for sucrose accumulation permitted qualitative analysis of the trait and indicated monogenic recessive control, although deviations from Mendelian inheritance were observed in some populations. This major gene, designated <jats:italic>sucr</jats:italic>, was mapped in F<jats:sub>2</jats:sub>, F<jats:sub>3</jats:sub>, and BC<jats:sub>1</jats:sub>F<jats:sub>2</jats:sub> populations using a set of 95 informative RFLP and isozyme markers covering the tomato genome. A map location near the centromere of chromosome 3 was established, with tight linkage to the genomic clone TG102. Association of sucrose accumulation with yellow fruit, encoded by an allele of the <jats:italic>r</jats:italic> gene, permitted alignment with the classical map, thereby confirming the map location of <jats:italic>sucr</jats:italic>. A linkage map of the region surrounding <jats:italic>sucr</jats:italic> was obtained by monitoring recombination between flanking markers in the back‐crosses to tomato. A cDNA clone of tomato fruit acid invertase, TIV1, was mapped to TG102 and <jats:italic>sucr</jats:italic>, with no recombination between the two RFLP markers observed in over 1700 meiotic products. Despite the tight linkage, TG102 and TIV1 hybridize to distinct restriction fragments, hence do not represent the same gene. The genetic data strongly suggest that <jats:italic>sucr</jats:italic> is an allele of the invertase gene and thus support previous biochemical studies that demonstrated low invertase activity in sucrose‐accumulating fruit. <jats:italic>L. hisutum</jats:italic>, another low‐invertase, sucrose‐accumulating species, was hybridized with <jats:italic>L. chmielewskii</jats:italic> and the resulting F<jats:sub>1</jats:sub> plants accumulated sucrose, indicating that genetic control of soluble sugar composition is conserved in these two species.</jats:p>

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