Inbred backcross breeding for soluble solids and the identification of correlated molecular markers in tomato: Update

Triano, S.R. and St. Clair, D. A. Dept. Veg Crops, Univ. Calif. Davis, CA 95616

The inbred backcross (IBC) breeding method (Bliss, 1981) was used to develop a set of 106 IBC lines (Lycopersicon esculentum cv. UC 204B X Lycopersicon cheesmanii f. minor). IBC breeding is being tested as a way to introgress favorable genes controlling soluble solids from a wild species into an adapted California processing tomato cultivar (UC 204B), and to establish correlations between molecular markers and genes controlling quantitatively inherited traits (QTLs). Correlated markers will be tested in indirect selection studies to improve solids in this and a related population. The experimental design of this project has been previously reported (Triano and St. Clair, 1992).

Each of the 106 lines has been evaluated for fruit soluble solids, pH and weight in a randomized complete block design with 4 blocks at each of 3 locations over 2 years, 1991 and 1992. Based on analyses of variance and means separations, we have identified 14 lines with significantly improved soluble solids, good pH and acceptable fruit weight (Table 1). The mean soluble solids values of these selected lines ranged from 5.55 to 6.49 deg. Brix. For comparison, UC204B averaged 5.15 deg. Brix and FM 785 averaged 5.57 deg. Brix. The minimum acceptable fruit weight was not significantly less than Peto 95-43, a small-fruited processing tomato cultivar.

These data are being combined with molecular marker data to determine correlations between quantitatively inherited traits and previously mapped molecular markers (Tanksley et al., 1988) estimating probable QTL locations in the genome. Correlated markers will ultimately be tested for their predictive value as indirect selection markers for QTLs to improve soluble solids in tomato populations.

Table 1. Summary of Tukey's means separations on 14 selected lines compared to the recurrent parent (UC 204B) and Peto 95-43.

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Number of progeny lines         Deg. Brix    pH      Fruit Weight (g/20 fruit)
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Greater than UC 204B                14        1                   0
N.S.D. from UC 204B                  0       13                   3
N.S.D. from Peto 95-43             ---      ---                  11
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N.S.D. = not significantly different at P <= 0.05

Acknowledgments

We would like to thank Gene Miyao (Yolo and Solano Counties Farm Advisor) and Bob Mullen (San Joaquin County Farm Advisor) for arranging field space with our grower cooperators, Danny Merkley and Richard Marchini. We also thank Harris Moran Seed Company for donating additional field space and assistance.

Literature Cited

Bliss, F. A. 1981. Utilization of vegetable germplasm. HortScience 16: 3-6.
Tanksley, S. D., J. Miller, A. Paterson and R. Bernatzky. 1988. Molecular mapping of plant chromosomes. In J.P. Gustafson and R. Appels, eds., Chromosome Structure and Function - Impact of New Concepts, Proceedings of the 18th Stadler Genetics Symposium, Plenum Press, New York, pp. 157-173.
Triano, S. R. and D. A. St. Clair. 1992. Inbred backcross breeding for soluble solids and the identification of correlated molecular markers in tomato. TGC Report 42: 40-42.