INTROGRESSION INTO TOMATO (LYCOPERSICON-ESCULENTUM) OF THE L-CHMIELEWSKII SUCROSE ACCUMULATOR GENE (SUCR) CONTROLLING FRUIT SUGAR COMPOSITION

High sucrose concentration in fruit of Lycopersicon chmielewskii is go verned by the recessive sucrose accumulator gene (sucr) that is situat ed in the pericentromeric region of chromosome 3. The suer gene was in trogressed into the genetic background of the hexose-accumulating cult ivated tomato (L. esculentum cv 'Hunt 100') by marker-assisted selecti on using tightly linked RFLP markers and a tomato acid invertase cDNA as probes for sucr. RFLP mapping indicated that the segment containing sucr comprised over 43.2 cM in the BC1F2 generation, representing ove r one-third of the total length of chromosome 3. By selecting for cros sovers between suer and the flanking visual marker r (yellow fruit fle sh) and RFLP marker TG288, we were able to reduce the size of the sucr introgression fragment to 0.8-7.1 cM by the BC5 generation. Smaller r ecombinant fragments were not obtained despite screening a large BC6F2 population. The smallest sucr introgression reduced recombination bet ween the flanking visual markers sy (sunny) and bls (baby lea syndrome ) by 38%. To facilitate future introgression and recombination experim ents, a PCR-based test for the suer gene was developed using primers s pecific to the tomato invertase gene. This assay takes advantage of a small deletion that maps to the second intron of the L. chmielewskii i nvertase gene. The assay detected significant allelic variation both w ithin and between hexose- and sucrose-accumulating Lycopersicon spp.