sucr : Gene Symbol for the Reducing Sugar vs. Sucrose Accumulation Character in Tomato Fruit.

Stommel, J.R. USDA-ARS, Beltsville, MD

Sucrose accumulation in tomato fruit was first reported by Davies (1966) in accessions of the green fruited species Lycopersicon peruvianum, L. hirsutum and L. hirsutum var. glabratum and more recently in L. chmielewskii (Yelle et al. 1988). The cultivated tomato (Lycopersicon esculentum Mill.) and related wild species which bear red or orange pigmented fruit (L. esculentum var. cerasiforme, L. pimpinellifolium, and L. cheesmanii) are characterized by an accumulation of reducing sugars as the predominant fruit soluble carbohydrate (Davies 1966; Garvey and Hewitt 1991). Recent studies suggest that sucrose accumulation may condition higher levels of soluble solids (Yelle et al. 1988, 1991; Stommel 1992). Since sugars are a major component (55-65%) of the soluble solids fraction of tomato fruit, they have a direct influence on tomato processing quality. The high levels of total sugars and soluble solids found in many accessions of the green fruited tomato species has suggested an attractive opportunity to increase soluble solids levels in L. esculentum via interspecific transfer of the sucrose accumulation character.

Current efforts have examined the genetic control of reducing sugar vs. sucrose accumulation in tomato fruit. An analysis conducted on the inheritance of fruit sugar type using populations derived from a L. esculentum x L. chmielewskii cross (Yelle et al. 1991) demonstrated significant deviation from models consistent with simple Mendelian inheritance. The distorted segregation noted in that study may be attributed to linkage between genes which influence sucrose accumulation and sterility in the derived plant materials. In a more recent study, tomato fruit sugar content was analyzed in F1, F2 and backcross populations derived from a cross of L. esculentum x L. hirsutum (Stommel and Haynes 1993). The observed segregation patterns for fruit sugar type in all populations are consistent with those expected for a single gene dominant for a high percentage of reducing sugar and clearly demonstrate monogenic inheritance for this character. For future reference, the symbol sucr is proposed to designate the gene conditioning tomato fruit sugar type. The results of this study also demonstrate that sucrose accumulation per se is not essential to transfer increased soluble solids levels from L. hirsutum. Factors independent of sucrose storage positively influenced soluble solids content in the populations developed. Fruit glucose/fructose ratios were shown to be inherited independently of fruit sugar type and were influenced by at least two pairs of alleles.

Literature cited

Davies, J.N. 1966. Nature 209:640-641.
Garvey, T.C. and J.D. Hewitt 1991. J. Amer. Soc. Hort. Sci. 116:77-79.
Stommel, J.R. 1992. Plant Physiol. 99:324-328.
Stommel, J.R. and K.G. Haynes 1993. J. Amer. Soc. Hort. Sci. 118:In press.
Yelle, S., J.D. Hewitt, N.L. Robinson, S. Damon and A.B. Bennett 1988. Plant Physiol. 87:737-740.
Yelle, S., R.T. Chetelat, M. Dorais, J.W. DeVerna and A.B. Bennett 1991. Plant Physiol. 95:1026-1035.