Submitted to: Experiment Station Bulletins
Publication Type: Experiment Station
Publication Acceptance Date: July 1, 2007
Publication Date: July 12, 2007
Citation: Chen, M.H., Bergman, C.J., Fjellstrom, R.G. 2007. Rice Waxy gene: Associations with apparent amylose content and pasting properties. Experiment Station Bulletins. http://beaumont.tamu.edu/eLibrary/Newsletter/2007_Highlights_in_Research.pdf. p. XV.
Rice end-use quality is strongly impacted by apparent amylose content (AAC). For example, the conventional long-grain rice in the US has intermediate AAC, and after cooking the rice is firm and fluffy in texture; while the conventional medium-grain rice has low AAC, and the texture of the cooked rice is soft, moist and sticky. The Waxy gene on chromosome 6 encodes the granule-bound starch synthase enzyme and controls much of the variation in rice AAC. The AAC, however, does not explain all the variation in rice processing characteristics. Some varieties with similar AAC have very different pasting viscosities and processing properties. For example, Dixiebelle, a high AAC-type, has a stronger pasting curve than some other high AAC-types and has a superior processing property. The Waxy gene reportedly has major effects on starch-pasting properties. We investigated the sequence variations in the Waxy gene and their associations with AAC and pasting properties using 171 rice accessions originating from 43 countries in an effort to develop molecular markers for grain-quality traits. Three sequence variation sites in the Waxy gene, intron 1, exon 6 and exon 10, were genotyped and the combination of these sequence variations generated four alleles. The allele 1 associated with low AAC-, allele 2 associated with intermediate AAC-, and allele 3 and 4 correlated with high AAC-type rice accessions. A mean comparison of each parameter of the RVA pasting curve demonstrated that rice accessions containing the Waxy allele 4 type had significantly higher hotpaste, coolpaste and setback viscosities (alpha=0.05) than all the other allele-types regardless of their AAC. The difference between allele 4 from all other alleles is the sequence variation in exon 10 of the Waxy gene. Molecular markers developed for this sequence variation site would be able to assist breeding programs selecting for specialty rice with superior processing properties.