Isolating genes for a quantitative trait: A case study involving total and soluble solids in tomatoes
Kim, Doo-Hwan
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https://hdl.handle.net/2142/23050
Description
Title
Isolating genes for a quantitative trait: A case study involving total and soluble solids in tomatoes
Author(s)
Kim, Doo-Hwan
Issue Date
1990
Doctoral Committee Chair(s)
Juvik, John A.
Department of Study
Biology, Genetics
Discipline
Biology, Genetics
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Genetics
Language
eng
Abstract
Soluble solids in tomatoes are very important in processing tomatoes because a slight change can dramatically decrease the energy cost for dehydration of tomato puree into concentrated sauces and paste. Fresh market tomatoes with high sugar and organic acid content are preferred by consumers.
In this study, Wehrhahn and Allard's inbred-backcross procedure was employed to isolate and analyze major genes controlling quantitative variation for chemical components of tomato solids; such as pH, refractive index, percent dry weight of puree and serum, citric acid, glucose and fructose. Inbred-backcross populations were developed by two successive backcrosses of high soluble solids line (LA1501) to the commercial tomato cultivar (VF145B-7879) followed by four selfing generations to achieve 67 near homozygous lines. These tomato lines were grown in the field and harvested both at red-ripe and breaker stage. The breaker fruits were ripened under a controlled environment until red-ripe. Both sets of ripe fruits were analyzed. The results of this study showed that two parents differed significantly in all components except citrate. Soluble solids are the major portion of total solids (about 75%) and differences in total solids between the parents were came primarily (about 80%) from the soluble fraction. Total sugar content accounted for about 50% of the differences in total solids and 65% of the differences in soluble solids between the two parents.
In our studies, the performance of inbred-backcross derived lines for total and soluble solids were grouped by 95% confidence intervals, uncovering individual SGD classes. Two SGD groups were identified for total and soluble solids, glucose and pH, and one SGD group for fructose. The inbred-backcross procedure was successful at isolating and identifying individual genes controlling the differences in these components between the parents. We hypothesized that two different gene classes are controlling the physiological processes affecting solids content. One gene was associated with the assimilate accumulation at early stage of ripening while the other gene was involved in the other factors during ripening.
The results of the simulation study indicated that a modified inbred-backcross procedure with selection could produce more SGD lines. Selecting at random among the top 40 or 50% of the population increases the percentage of SGD about 50% compared to Wehrhahn and Allard procedure.
The newly created SGD inbred-backcross lines developed from this study can be used for basic genetic studies on tomato solids and for commercial purposes as breeding lines for the improvement in solids content. They may be excellent materials for use with RFLP markers as a next step.
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