Characterisation of a novel genetic contribution to the breadmaking quality of wheat

CONCLUSIONS

A DNA map of chromosome 3A has been developed within this project. A useful map of six microsatellite markers was obtained, but the degree of polymorphism found between Capelle-Desprez and Bezostaya I was disappointing. This was particularly the case for the long arm around the site of the putative loaf volume gene (Lvl 1) deduced from this work.

A single gene designated Lvl 1 (after loaf volume) appears to be responsible for controlling loaf volume, crumb colour and crumb score. It is located on the long arm of chromosome 3A about 30 to 40 map units from the centromere. It is closely associated with a gene determining gel protein weight. It is possible that this gene could still be Lvl 1 rather than a separate gene.

A Quantative Trait Locus, which is likely to be a single gene controlling Falling Number, is located on the short arm very close to the centromere.

A gene (or genes) affecting gel protein G' is located on a chromosome other than 3A and is a consequence of too few backcrosses in the development of the substitution line.

The analysis of the single substitution lines between the donor Bezostaya I and recipient Capelle-Desprez has confirmed that Group 1 chromosomes of Bezostaya I improve many dough rheological properties compared with those of Capelle-Desprez.

Single chromosome substitution studies confirmed the adverse effects of 3A and identified a similar influence of 3B on protein strength parameters. It appears that the effect of 3B matches that of 3A but in some cases exceeds its potency.

Group 7 chromosomes also appear to be contributors to protein quality. These may be candidates for further detailed study.

This study has added further information to the genetic basis of breadmaking quality but has also shown that environment exerts a major effect (i.e. the 'German effect' where the poor quality recipient Capelle-Desprez grown in eastern Germany produced significantly better loaf volume than the UK-grown equivalent.

IMPLICATIONS and BENEFITS

The DNA marker map of chromosome 3A produced by this project will be useful to breeders concerned with any quality traits controlled by this chromosome. The traits include an influence on loaf volume which means that the results will be of value to the wheat production and usage chain.

A new gene has been found which contributes to the regulation of alpha-amylase activity in grain. Control of this factor is important to the supply of UK wheat and its use.

Although not discussed in this project, benefit to the UK breeding and farming communities has been generated in terms of resistance to ear blotch since a single-gene resistance to Septoria tritici was located on chromosome 3A of Bezostaya I during the course of the study.

Abstract

The molecular basis for the role of protein and non-protein components of breadmaking wheat in determining the processing properties is not fully understood. Previous work performed at John Innes Centre on single chromosome substitution lines had identified chromosome 3A as having influence on the flour parameters related to breadmaking quality. However, the biochemical factors that mediated the observed chromosomal effects were not identified. Studies have suggested that 'soluble' or non-prolamin proteins, i.e. mainly albumins and globulins, which influence breadmaking quality are linked with chromosome 3A. Biochemical studies using single chromosome substitution and recombinant lines to determine the relationship between specific soluble proteins and quality parameters that are influenced by chromosome 3A could be used as a basis for identifying suitable markers for breadmaking quality of wheat.

During mechanical mixing a number of physical and chemical processes occur that result in the modification of the gluten structure. In particular, disulphide-sulphydryl interchange reactions occur reducing the stress within the dough. The inclusion of an oxidising agent creates new reaction possibilities and tends to favour the formation of inter-glutenin disulphide bonds thus stabilising the dough. At the molecular level, mixing creates and breaks bonds within high molecular weight glutenins: de-polymerisation forms smaller glutenin subunits which then reform to some extent. The rheological properties of bread dough, therefore, play an important role in the behaviour of dough during processing. They have been shown to exert a major influence on the quality of the final baked product and on the mixing energy required to produce optimal breadmaking performance. Rheological properties predict the ability to retain the gas produced during fermentation and ensure a satisfactory balance between viscosity (i.e. flow during expansion) and elasticity (i.e. the ability to retain shape). For this reason, the rheology of wheat dough is routinely tested by millers and bakers to check against flour specifications, classify flour samples into broad quality groups, i.e. ensure general "fitness for purpose", and thus identify gross flour faults which would result in severe processing problems within a plant. However, correlations with breadmaking quality are relatively poor and such measurements cannot replace breadmaking quality assessment.

In this study the genetic contribution to the breadmaking quality of wheat was evaluated in two breadmaking systems; the Chorleywood Bread Process (in which the dough is mixed to fixed energy) and a spiral mixer no-time dough (in which the dough is mixed to fixed time). Sets of Cappelle (Bezostaya) single chromosome substitution lines of wheat, together with the two parent wheats, and a population of 48 chromosome 3A recombinant lines were grown for the 1998 harvest at the JIC site at the Morley Research Centre. The growing of these sets was repeated for the 1999 harvest at three sites in the UK and two in Eastern Germany. Two of the UK sites were JIC sites at Morley and in Bawburgh, and the third was a Nickerson UK Ltd site at Bury St Edmunds. One of the German sites was at the University of Halle and the other was owned by PBI Ltd. The set of chromosome 3A recombinant lines, derived from Cappelle-Desprez (Bezostaya 3A) line, plus the parent wheats, were grown for the 2000 harvest at the two JIC sites and the Nickerson UK Ltd site.

AIMS

To increase knowledge of the relationship controlled by chromosome 3A between biochemistry and breadmaking quality in wheat, in the context of near-commercial milling and baking techniques.

To characterise genetically the novel 3A influence on breadmaking quality.

To identify a tagging diagnostic marker (possibly DNA based, but could be biochemical or morphological), for easy selection of breadmaking quality, for use by wheat breeders.

To identify the biochemical mechanism through which chromosome 3A affects breadmaking, and establish this as a flour quality test, if appropriate.