Investigating the role of flavonoid biosynthesis in coat-imposed dormancy to facilitate the breeding of white-grained varieties of wheat

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The vast majority of bread consumed in the UK, whether made from white, brown or wholemeal flour, is produced from red-grained wheat. The 'red' colour of the grain (actually more of a reddish-brown) is due to the presence of coloured compounds, called flavonoids, in the seed coat. As well as colour, these flavonoids (related to the tannins found in tea and red wine) give wholemeal bread its somewhat bitter taste that is disliked by many people. For this and other cultural reasons, most bread produced in the UK and Europe is made from white flour, which has had all of the outer layers of the seed (the bran) removed during milling. However, removal of the bran results in a reduction in the nutritional quality of the grain, as much of the fibre, minerals, vitamins and other nutrients of the wheat grain are found in these outer layers. There is overwhelming evidence that consumption of wholemeal bread and wholegrain products containing these components contributes to a healthier lifestyle by offering protection against a number of diseases including diabetes, heart disease and bowel cancer. However, surveys suggest that one third of British adults and a quarter of children do not eat any wholegrain foods at all, and promotion of the health benefits of wholemeal grains has had relatively little effect on this sector of the population. White-grained wheats lack the red flavonoids of the seed coat and the associated bitter taste; wholemeal bread made from white-grained varieties has therefore been found to be more acceptable to some consumers; there also an appreciable market for wholegrain breakfast cereals, cakes and biscuits made from white wheat. Although white wholegrain products lack the health benefits imparted by the tannin components, they still contain far more fibre, micronutrients and phytochemicals than those made from refined flour. However, nearly all wheat varieties grown in the UK are of the red-grained type, as white grains are prone to germinating before harvest, a particular problem in countries such as the UK where cool, wet weather before harvest is common. This 'pre-harvest sprouting' results in a loss of grain quality and even a small proportion of sprouted grains can result a serious loss of value for the crop. For this reason, white-grained wheats are mainly grown in warmer, drier parts of the world such as Australia, necessitating the costly importation of grain by UK millers and bakers. In an existing programme that involves other academic partners as well as most of the UK's commercial wheat breeders, our colleagues are studying the underlying biology of pre-harvest sprouting. This current work is leading to the identification of UK wheat varieties that are more sprouting resistant and should provide information that will help breeders to improve their performance still further. Our new project has several aims: first, we want to develop genetic markers for the genes that confer the white grain colour, so that wheat breeders can more easily produce new white varieties with good sprouting resistance. Second, we want to establish whether breeding white grain colour into the sprout-resistant varieties identified above will generate sprouting-resistant white wheat lines that can withstand the UK's cool, wet climate. Finally, we want to explore the possibility that compounds earlier in the biochemical pathway that produces the red pigment are protective against sprouting, in which case we should be able to develop white wheats that are as sprout-resistant as red-grained varieties and also retain the antioxidant properties of the flavonoids. This project thus aims to provide the knowledge and tools to facilitate the development of white-grained wheats that can be grown reliably under UK conditions.