INHERITANCE AND GENETIC-MAPPING OF FRUIT SUCROSE ACCUMULATION IN LYCOPERSICON CHMIELEWSKII

Fruit of the domestic tomato (Lycopersicon esculentum Mill.) accumulat e soluble sugars primarily in the form of the hexoses, glucose and fru ctose. In contrast, the predominant sugar in fruit of the wild tomato relative, L. chmielewskii, is sucrose. In the present study, the inher itance and linkage relations of sucrose accumulation were examined in interspecific L. esculentum x L. chmielewskii populations. In backcros ses to either the wild or domestic tomato, segregation for sucrose acc umulation permitted qualitative analysis of the trait and indicated mo nogenic recessive control, although deviations from Mendelian inherita nce were observed in some populations. This major gene, designated suc r, was mapped in F-2, F-3, and BC1F2 populations using a set of 95 inf ormative RFLP and isozyme markers covering the tomato genome. A map lo cation near the centromere of chromosome 3 was established, with tight linkage to the genomic clone TG102. Association of sucrose accumulati on with yellow fruit, encoded by an allele of the r gene, permitted al ignment with the classical map, thereby confirming the map location of sucr. A linkage map of the region surrounding sucr was obtained by mo nitoring recombination between flanking markers in the backcrosses to tomato. A cDNA clone of tomato fruit acid invertase, TIV1, was mapped to TG102 and sucr, with no recombination between the two RFLP markers observed in over 1700 meiotic products. Despite the tight linkage, TG1 02 and TIV1 hybridize to distinct restriction fragments, hence do not represent the same gene. The genetic data strongly suggest that sucr i s an allele of the invertase gene and thus support previous biochemica l studies that demonstrated low invertase activity in sucrose-accumula ting fruit. L. hisutum, another low-invertase, sucrose-accumulating sp ecies, was hybridized with L. chmielewskii and the resulting F-1 plant s accumulated sucrose, indicating that genetic control of soluble suga r composition is conserved in these two species.