Optimising grain shape and size for improved processing quality

Milling is the process by which wheat is ground into flour, during which the wheat grain is separated into its different parts: the outer layers (bran), embryo (germ) and endosperm (white flour). Milling wheat or barley is particularly difficult because of the irregular shape of the grain: unlike rice which is more-or-less cylindrical, wheat and barley have a deep groove or crease on one surface; this makes separation of the endosperm from the outer layers problematical. Different wheat varieties yield different types of flour for bread or for biscuit making but the amount of flour extracted from each grain also differs. Work has shown that yield of flour per grain is dependent on grain size and also shape, as this determines the proportion of the grain that is taken up by the endosperm relative to other grain parts. Moreover, with the recent uptake of de-branning (removal of the outer layers) by flour mills, the importance of the shape and depth of the crease to flour extraction has become very significant. Breeders routinely select new varieties for improvements in grain yield, a component of which is grain size, but have not previously selected specifically for grain shape. This project aims to survey the range of different grain sizes and crease shapes that exist in varieties of wheat and to relate them to milling yield. Grain shape is also important for barley used for malting (sprouting) where short fat grains are desirable since this allows starch present in the endosperm to be more rapidly used as food for the sprouting embryo. One ancient sub-species of wheat that was grown in India and Pakistan has small spherical grains with a very shallow crease; part of our work will be to assess what effect this extreme shape has on de-branning and milling and to study how its characters behave when crossed into the high yielding modern varieties. Similar mutations are also known in barley. Little is known however, about the genes that may be controlling these mutations or the development of the wheat or barley grain; as a first step to identify them we will use conventional genetic mapping techniques to locate them on the wheat and barley chromosomes. This will enable us to develop DNA markers linked to them, which can be used by breeders to select for a better grain shape in new varieties. While seeds from different species of plants may look very different, many scientists believe that the basic underlying developmental processes that give rise to them are shared; it is suggested genes that are found in one species which are proved to have major effects on development could have a direct counterpart in other species. We aim to use our own information on such genes from the model species Arabidopsis and maize to identify those potentially involved in wheat or barley for our use to modify grain shape and size to our advantage as well as to obtain information on how the process of grain development occurs.

This programme aims to optimise end user quality traits in wheat and barley. Milling yield is dependent on size and shape of grains and on the proportion of endosperm to the other tissues in the grain. The recessed ventral groove of wheat is a particular obstacle to the efficient extraction of the white flour and the adoption of new de-branning technology in UK mills has further increased the importance of crease morphology. For barley, a short, fat grain is desirable to assist water uptake and rapid starch mobilisation during malting. We will use forward and reverse genetics approaches combined with knowledge of seed development in model systems to improve our understanding of grain size and shape. This programme involves the major laboratories presently engaged in research in grain and seed development in the UK, together with a leading group working on milling technology allowing the benefits of altered grain shape to milling yield and malting quality to be assessed. We have shown that UK wheat varieties differ in grain morphology and will extend our analysis to broader germplasm including T. aestivum sphaerococcum which has rounded grains and a reduced crease. Introgression of the 'sphaerococcum' phenotype into elite UK material will allow the effects on de-branning and milling yield to be determined. The segregation of QTLs for grain shape will be studied in different populations to identify linked markers. We will also map and identify genes that may be controlling a similar (globosum) phenotype in barley. Our work in the model species Arabidopsis and maize is resolving the processes and genes that are involved in cell proliferation and differentiation in the endosperm. We hypothesise that cereal orthologues of these genes may underlie QTLs for grain size and shape. The expression of selected candidates will be altered in transgenic wheat or through TILLING in barley and an assessment of grain morphology and quality traits compared to parental lines.