Submitted to: Euphytica
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/18/2003
Publication Date: 6/7/2003
Citation: LARKIN, P., MCCLUNG, A.M., AYRES, N.M., PARK, W.D. THE EFFECT OF THE WAXY LOCUS (GRANULE BOUND STARCH SYNTHASE) ON PASTING CURVE CHARACTERISTICS IN SPECIALTY RICES (ORYZA SATIVA L.). EUPHYTICA 131:243-253. 2003. Interpretive Summary: The chemical constituents of the rice grain impact its cooking and processing quality. Differences in concentration of these components will determine whether the rice cooks dry and flaky or soft and sticky. Cooking properties will effect how rice can be best used during instantizing and canning industrial processes. Knowledge of the genetic control of the chemical constituents of the rice grain will help breeders to develop new rice cultivars that meet the specific needs of the rice industry. This study demonstrated that cooking properties of rice starch are predominantly controlled by one gene, granule bound starch synthase. Different forms of this gene determine viscosity characteristics of rice starch during heating and cooling cycles which take place during cooking and industrial processing. Molecular markers can be used to select for different forms of this gene and result in the development of rice cultivars that have widely divergent industrial uses.
Technical Abstract: Starch structure and functionality have a significant impact on the utilization of cereal grains as food and feed. Starch viscosity characteristics are used to characterize rice cooking, processing and eating quality. In order to examine the genetics of viscosity characteristics, we developed molecular markers for five of the major enzymes involved in starch synthesis in the endosperm: granule bound starch synthase, soluble starch synthase, rice branching enzymes 1 and 3 and starch debranching enzyme. These markers were polymorphic in a cross between two specialty rice varieties, Rexmont and Toro 2, which have divergent amylose contents and viscosity characteristics. An analysis was made of several hundred random F5 and F7 families for amylose content and pasting properties. The results indicated that the Waxy locus, encoding the gene for granule bound starch synthase, has a significant effect on peak viscosity, hot paste viscosity, cool paste viscosity, breakdown and setback viscosity. The locus for soluble starch synthase, which is linked to granule bound starch synthase, had a minor effect whereas rice branching enzymes 1 and 2 and starch debranching enzyme had no effect on pasting properties. These results demonstrate the overwhelming importance of genetic variation at the granule bound starch synthase locus on controlling rice cooking and processing quality.