High soluble-solids content in large-fruited tomato lines derived from a wild green-fruited species

An attempt was made to combine the high soluble-solids content of ripe fruits of the small, green-fruited Lycopersicon minutum with the horticulturally desirable characteristics of a standard L. esculentum cultivar. By backcrossing from the former to the latter, and by subsequent pedigree selection, pure-breeding lines in which soluble-solids content was elevated to 7-7.5 per cent—at least 2 percentage points above that of the recurrent parent—were synthesized. The new lines are comparable with the recurrent parent in size, color, and shape of fruit, plant habit, and yield, although they suffer from fruit softness, perishability, and other defects. The recombination of high soluble-solids content and large fruit size was achieved despite a moderately strong negative correlation (r = -0.46 in BC1) between these characters. Genetic linkages between soluble solids and a dominant delta-carotene character (possibly Del) as well as with the uniform ripening of unripe fruit (u) were also detected and broken by the backcross selection procedure. Additionally, soluble solids tended to be associated with several severe fruit-cracking defects. The continuous nature of distributions of soluble solids in the segregating generations, the linkage of solids content with several genetically independent characters, and the recapture of only part of the minutum genotype determining high soluble solids point to a complex, polygenic inheritance of this character. Several of the derived lines carry Ip, a dominant gene for intense fruit pigmentation evidently derived from L. minutum. A foliage variegation character of undetermined inheritance, and rv-4, a gene for reticulated virescence, also appeared de novo in the segregating generations, probably originating from mutation as deduced from genetic criteria. Appropriate genetic tests proved the existence of the r and y fruit pigmentation genes or similar alleles at the same loci in the minutum parent. The genetic difference between the parental species for certain fruit quality characteristics is thereby characterized.