Author
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Graybosch, Robert |
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Submitted to: Meeting Abstract
Publication Type: Abstract Only Publication Acceptance Date: 6/15/2008 Publication Date: 9/5/2008 Citation: Graybosch, R.A. 2008. Progress toward breeding waxy (amylose-free) wheats for the Great Plains of North America. Page 598, In: Jaime Prohens and Maria Luisa Badens, eds. Modern variety breeding for present and future needs. Editorial Universidad Politecnica de Valencia, Valencia, Spain. Interpretive Summary: Technical Abstract: In hexaploid wheats, three independent loci (Wx-A1, Wx-B1 and Wx-D1) encode production of the granule-bound starch synthase (GBSS) also known as the “waxy” protein. Waxy, or amylose-free wheats, have been developed via combination of null mutations at all three loci (Nakamura et al., 1995). Wheat lines carrying null mutations at either one or two of the Wx loci produce intermediate levels of starch amylose, and have been termed “partial waxy” (Nakamura et al., 1993). Null mutations at the Wx-A1 and Wx-B1 loci are fairly common; mutations at the Wx-D1 locus are rare (Graybosch, 1998). In the late 1990’s, breeding efforts were initiated to develop waxy winter wheats for the northern Great Plains of the USA. The breeding program has combined the natural occurring mutations found in the partial waxy wheats Kanto 107 (from Japan), BaiHuo (from China) and Ike (from Kansas, USA) with genes for agronomic adaptation and disease resistance from North American hard and soft winter wheats. In 2003, average grain yields of waxy breeding lines in Nebraska environments were 72% of Millennium, currently the most widely grown wild-type cultivar. By 2007, average grain yields of waxy breeding lines had reached 90% of Millennium. In both 2006 and 2007, average grain yields of NX04Y2107, the highest yielding waxy line, were not significantly different from that of Millennium. In a separate study, grain yields of waxy wheat were compared to those of all 6 possible partial waxy genotypes, and to wild-type, in four genetic populations. Grain yields averaged over two harvest seasons showed no significant differences in grain yield of waxy wheats relative to wild-type cultivars. Identical results were obtained both within all four populations, and across populations. Some differences were noted amongst partial waxy genotypes, but no consistent trends were noted. In addition, no differences in levels of tolerance to pre-harvest sprouting were detected within or across populations. Results suggest there is no grain yield penalty associated with the production of amylose-free endosperm starch, and that waxy wheat cultivars with grain yields equal to those of wild-type wheats will be attainable. |
