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United States Department of Agriculture

Agricultural Research Service

Title: Occurrence of the Waxy Alleles Wxa and Wxb in Waxy Sorghum Plant Introductions and Their Effect on Grain Thermal Properties

Authors
item Pedersen, Jeffrey
item Graybosch, Robert
item Funnell-Harris, Deanna

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 4, 2007
Publication Date: September 1, 2007
Citation: Pedersen, J.F., Graybosch, R.A., Funnell, D. 2007. Occurrence of the waxy alleles wxa and wxb in waxy sorghum plant introductions and their effect on grain thermal properties. Crop Science 47:1927-1933.

Interpretive Summary: Grain endosperm usually contains two types of starch, amylose and amylopectin, but some varieties or hybrids have endosperm with nearly pure amylopectin starch giving them unique properties for industrial and food applications. This is usually attributable to the absence of the enzyme granule bound starch synthase (GBSS) that is responsible for producing amylose. Grain without amylose has the texture or appearance of paraffin when broken and is therefore called "waxy". Although the existence of waxy sorghum has been recognized for decades, we recently discovered that this phenomena can be caused by two different alleles, one of which (wxa) is associated with no detectable GBSS, and the other (wxb) which is associated with apparently inactive GBSS. In this paper, the occurrence of the wxa and wxb alleles in the USDA-ARS photoperiod-insensitive sorghum collection was determined, and the effects of the wxa and wxb alleles on thermal properties of sorghum starch measured by differential scanning calorimetry. Of the 51 purported waxy accessions examined, twenty four of the 28 accessions were confirmed to be waxy by negative iodine staining for amylose had no detectable GBSS (wxa), and four were show to contain GBSS (wxb). Gelatinization temperatures were lower for wild-type sorghum grain than either of the two waxy types. Mean gelatinization onset temperature was slightly higher for waxy lines with the wxb allele than for waxy lines with the wxa allele. Considerable variation in gelatinization temperature was observed within all types of sorghum grain, suggesting a role for additional modifier genes affecting sorghum starch structure and utilization.

Technical Abstract: The existence of two waxy alleles, wxa associated with no detectable Granule Bound Starch Synthase (GBSS), and wxb associated with apparently inactive GBSS was recently reported in sorghum (Sorghum bicolor L. Moench). In this paper, the occurrence of the wxa and wxb alleles in the USDA-ARS photoperiod-insensitive sorghum collection was determined, and the effects of the wxa and wxb alleles on thermal properties of sorghum starch measured by differential scanning calorimetry. Of the 51 purported waxy accessions examined, 14 tested positive for presence of amylose and were considered to be previously misclassified wild-type lines. Nine accessions were mixed for presence or absence of amylose. Twenty four of the 28 accessions confirmed to be waxy by negative iodine staining for amylose had no detectable GBSS using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) (wxa), and four were show to contain GBSS (wxb). Mean gelatinization onset, peak, and end temperatures were significantly lower for wild-type than either of the two waxy genotypes. Mean gelatinization onset temperature was slightly higher for waxy/GBSS positive genotypes than waxy/GBSS negative genotypes. Mean gelatinization end temperature was slightly higher for waxy/GBSS negative genotypes than waxy/GBSS positive genotypes. Significant genetic variation was observed within genotypic classes, suggesting a role for additional modifier genes affecting sorghum starch structure or micro-environmental effects.

Last Modified: 7/31/2014
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