A segment from chromosome 7 of the wild tomato species, Lycopersicon chmielewskii has been introgressed through backcrossing into the processing cultivar, VF145B-7879. This segment was previously shown to carry a gene or genes that increase the soluble solids content in ripe red tomato fruits. To study the allelic interaction of this gene(s) and ascertain its performance in different genetic backgrounds, this line, homozygous for the L. chmielewskii segment, was crossed to its isogenic parent (VF145B-7879) and three other commercial cultivars (UC204c, E6203, and ChicoIII). The recurrent parent VF145B-7879 was also crossed to the other cultivars to generate two sets of hybrids, one heterozygous for the L. chmielewskii segment and the other homozygous for the L. esculentum segment on chromosome 7. Results from two years of field study revealed that the L. chmielewskii fragment, when either homozygous or heterozygous in the VF145B-7879 background, comparably increased soluble solids concentration in red fruit, suggesting dominant allelic interaction. This increase ranged from 8%–10% higher soluble solids content in these lines compared to the levels found in the recurrent parent (VF145B-7879). The F1 hybrids containing one dosage of this gene(s) showed a significant increase in the soluble solids content compared to the commercial parents. However, due to F1 heterosis observed in all the hybrid combinations, soluble solids content in the hybrids with this gene were not significantly greater than that of the hybrids without this gene. This gene was found to exert no significant influence on fruit pH, weight, and yield.
Gad G. Yousef, Shyh-Shyan Wang and John J. Juvik
Anne C. Kurilich, Shyh-Shyan Wang and John A. Juvik
Inbreds IL451b sugary1 (su1) and IL678a su1 isogenic for the sugary enhancer1 (se1) gene mutation were used to analyze the relationship between se1 gene dosage and endosperm sugar content. Each line was self-pollinated and reciprocal crosses were made between the isolines of each genotype to produce se1 gene dosages of 0, 1, 2, and 3 in the triploid endosperm. Ears were harvested at 15, 18, 21, 24, 27, and 45 days after pollination (DAP). Whole kernels were freeze-dried, ground into powder, and stored at –80°C until subsequent chemical analyses. Sucrose, glucose and fructose were analyzed using high-pressure liquid chromatography (HPLC), the results of which indicated a significant increase in kernel sugar content when the se1 allele is homozygous.
Sucrose content at 21 DAP (typical maturity for harvesting) was observed to increase in the IL451b and IL678a backgrounds from zero to three doses of se1 by 65% and 18% respectively, indicating that this mutation varies in its expression in different genetic backgrounds. Associations between kernel phytoglycogen and starch content and se1 gene dosage are presented. The biochemical lesion associated with the se1 gene product is discussed.