Ground Cover Supplement : GC Supplement - Wheat pre-breeding
18 GROUNDCOVER Issue 127 | March – April 2017 | GRDC GROUNDCOVERTM SUPPLEMENT: WHEAT PRE-BREEDING GRAIN QUALITY FAST FACT n Wheat quality has different meanings at each step of the value chain. To some, it equates to price; to others, it is the complexity of the genetics and processing systems used to produce the diverse range of flours needed to manufacture the array of end products demanded by consumers. Quality a key to profitability Grain-quality defects such as late maturity alpha-amylase (LMA) and black point have a genetic basis, allowing the incidence risk to be significantly reduced through breeding By Dr Gio Braidotti n There are genetic defects within the commercial wheat genepool that mostly lie dor mant – until triggered by certain environmental conditions. Two examples of this are late maturity alpha-amylase (LMA) and black point, which when activated lead to quality downgrades. Both are the subject of research at the University of Adelaide by Dr Daryl Mares and Dr Kolumbina Mrva, who were the first in the world to characterise LMA as genetic. Their approach involves understanding the environmental triggers well enough to replicate the conditions in controlled glasshouse or field trials. This approach allows them to benchmark Australian wheat cultivars and advanced breeding material for susceptibility to LMA and black point, while also identifying sources of resistance. Their ultimate aim is to characterise the genetic basis of resistance to these inducible grain-quality defects and work up the molecular markers that allow wheat-breeding companies to exclude the genetic defects in future cultivars. For both LMA and black point, Dr Mares’s research group is on track to achieve both goals. LATE MATURITY ALPHA-AMYLASE For LMA, the likely field environmental trigger is a cool temperature shock midway between flowering and harvest ripeness. It results in unacceptably low falling number, which causes a downgrade in grain classification at receival. Dr Mares says that effective screening technologies – including molecular markers for several genetic sites that contribute to LMA susceptibility – have been developed in collaboration with Dr Judy Cheong (South Australian Research and Development Institute) and are used to support wheat variety development and classification. “Currently, wheat breeders do not necessarily know which breeding parents carry LMA and this represents a barrier to the most effective and widespread use of the markers,” Dr Mares says. “But we are confident that in the near future we will have identified the genes involved and be able to develop diagnostic markers.” Previously, LMA-prone material could not be detected until late stages of development when the germplasm had incurred almost the full costs of creating a new variety. Sometimes, the defect was not noticed until the wheat was growing in far mers’ paddocks. The research in Dr Mares’s group will make it possible to detect and cull LMA-prone material early in the breeding cycle, thereby significantly reducing breeding costs and preventing the loss of high-performing material late in its development. “In addition we use the screening facilities for ongoing research,” he says. “That means we are starting to understand the mechanisms involved and the complex TABLE 1 Summary of key findings of research on yellow pigmentation. Compound and role Finding LUTEIN Predominantly responsible for yellow pigment in bread and durum wheat at harvest ripeness Lutein becomes more stable when it is chemically altered (esterified) by a thermostable enzyme. Warm, dry storage conditions for optimum esterification and lutein stability have been identified. The gene encoding the lutein-stabilising enzyme has been isolated and sequenced. A deletion of this gene results in zero ester formation. Analysed the genetic and environmental control of the proportion of grain colour compounds recovered during flour milling. Developed bread wheat with lutein content similar to durum that has attracted interest from noodle manufacturers in South-East Asia and Japan. LIPOXYGENASE (LOX) Degrades the natural yellow pigment lutein during end-product preparation Wheat varieties screened for variation in LOX expression. Detected: near zero levels (in a small number of synthetic hexaploid wheats as well as Kamilaroi durum) through to low to medium levels (Sunco, Cranbrook and durums Yallaroi and Wollaroi) and high levels (most bread wheats). Tested LOX activity in grain and flour produced by three cultivars across 27 sites in SA. Cultivar rankings were maintained despite substantial variation between sites, indicating a strong genetic influence. Used molecular markers to show that a naturally occurring mutation in one LOX gene accounts for a major part of the differences between high and low LOX wheats. ALPHA-TOCOPHEROL (VITAMIN E) Inhibits lutein loss by LOX A survey of wheat varieties indicated there is a twofold difference in total tocochromanol content. Unfortunately, nearly all the tocopherol is located in the embryo and is discarded during milling. POLYPHENOL OXIDASE (PPO) AND REACTIONS CAUSING DARKENING OF PRODUCTS Hides the yellow pigmentation and cause speckliness Earlier GRDC-funded work in collaboration with Dr Robert Asenstorfer, which complements the yellow pigment work, identified zero PPO germplasm along with the tools required by breeders for selection. Characterised a range of chemical and biochemical reactions that result in darkening and speckliness during end-product preparation.
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