Fgr, a major locus that modulates the fructose to glucose ratio in mature tomato fruits

A genetic trait determining the ratio of fructose to glucose in mature tomato fruits is described. A backcross breeding program based on the interspecific cross of Lycopersicon hirsutum and L. esculentum yielded stable genotypes with a high ratio of fructose to glucose (>1.5:1) compared with the approximately equimolar ratios found in L. esculentum. Two inter-simple- sequence repeat (ISSR) DNA sequences, highly associated (20 2, BC and F₃ populations from the cross between genotypes having high and low fructose to glucose ratios, suggested that the L. hirsutum-derived allele (Fgr ^H), which increases the fructose to glucose ratio, is partially dominant. Fgr ^H leads to an increase in fructose levels and a subsequent decrease in glucose levels, with no effect on total hexose levels. Accordingly, we conclude that the Fgr locus modulates the partitioning of hexose sugars between fructose and glucose, with no effect on total sugars or TSS. Received: 8 March 1999 / Accepted: 12 May 1999