The high-molecular-weight glutenin subunit compositions of wheat varieties bred in Finland

The composition of high-molecular-weight (HMW) glutenin subunits in 35 Finnish bread wheat cultivars was determined by SDS-polyacrylamide gel electrophoresis. One third of the varieties have one of two HMW glutenin subunit compositions and there are only 17 different compositions in all. Three cultivars, Antti, Kiuru and Panu, are genetically mixed for some of these subunits. Cultivar Tammi (II) contains a novel HMW subunit of glutenin, not detected in any bread wheat previously analysed, and is presumed to be coded by genes on chromosome 1A at the Glu-Al locus. On the basis of previous work, which related individual subunits to bread-making quality, HMW glutenin subunit quality (Glu-1 quality) scores were calculated for the varieties. The results are related to the bread-making quality ofFinnish


Introduction
The high-molecular-weight (HMW) sub- units of glutenin are synthesised in the devel- oping endosperm of wheat, which, at matur- ity, comprise some 10 % of the storage pro- tein of the grain.The subunits are coded by genes at three loci, Glu-Al Glu-BI and Glu- Dl, which occur on the long arms of chromo- somes IA, IB and ID respectively (Payne et  al. 1982).Each locus exhibits extensive allelic variation (Lawrence and Shepherd, 1980)  and this is partly responsible for the differ- ences in bread-making quality between culti- vars (Payne et al. 1981 a).The HMW sub- units of glutenin are best resolved by sodium dodecyl sulphate, polyacrylamide gel electro- phoresis (SDS-PAGE) and this is the estab- lished method of identifying and cataloguing the various subunits (Payne and Lawrence,  1983).The procedure can also be used in con- junction with aluminium lactate-PAGE, which fractionates the gliadin proteins, to identify cultivars and to determine which of them contain biotypes for storage proteins (Zillman and Bushuk 1979).
Table I.Finnish wheat cultivars, the name of the breeder, the pedigree and the year of cultivar release.In this paper, we have used SDS-PAGE to determine the HMW glutenin subunit com- positions of the 35 spring and winter wheat cultivars bred in Finland over the last 60 years.The results are related to the bread-making qualities of the varieties.

Materials and methods
Samples of 35 winter and spring wheat cul- tivars were obtained from the Finnish State Seed Testing Station.The cultivars, the name of the breeder, the pedigree and the year of cultivar release are given in Table 1.

SDS-PAGE
Total protein was extracted from segments of three grains of each cultivar and fraction- ated by SDS-PAGE using 10 % gels as de- scribed previously (Payne et al. 1980 and  1982).All the cultivars were extracted and analysed at least twice on separate gels.As described elsewhere (Payne et al. 1987) the presence or absence of subunit 2* cannot be determined for cultivars which contain subunits 2+12 but lack subunit 1.Such cul- tivars were additionally analysed using 5 % gels (Payne et al. 1981 b) which clearly re- solves subunit 2 from 2*.The numbering sys- tem for the HMW glutenin subunits is that described by Payne and Lawrence (1983).

Results
A typical fractionation of cultivar grain proteins by SDS-PAGE is shown in Fig. 1.The area of the gel containing the HMW sub- units of glutenin is marked by brackets and they have been given numbers according to standardised nomenclature (Payne and Lawrence, 1983).All the subunits but one in the set of 35 cultivars have been described previously.The exceptional subunit, found in cul- tivar Tammi (II), was assumed to be coded by genes on chromosome 1A at the Glu-Al locus because the cultivar contained its full alloca- tion of IB-and ID-encoded subunits, but none by chromosome IA.In addition, the subunit occurred as a thin band of slow mobility (Fig. 1, slot 4) typical of the commonly occurring 1A-encoded subunits 1 and 2* (Fig. 1, slots 3 and 5 respectively).It is proposed to number the subunit 25 and to call the allele Glu-Ald.This information will be included in the next update of the HMW glutenin sub- unit catalogue, with Tammi (II) as the stan- dard.
The HMW glutenin subunit compositions of the 35 cultivars are listed in Table 2. On the basis of analysing six grains per cultivar only, four cultivars (Antti, Kiuru, Panu and Tammi (II) were shown to consist of at least two biotypes with different HMW glutenin subunits.Antti and Kiuru each contained two alleles at Glu-Al, the predominant one coding for subunit 1 and the other, the null allele, which does not produce a subunit.The sample of Panu grain analysed was highly mixed, for it contained two alleles at all three Glu-1 loci.
Most of the cultivars analysed have also been given a HMW glutenin subunit quality (Glu-1 quality) score in Table 2.This was cal- culated by summing the scores assigned previously to individual subunits as shown in Table 3. Unfortunately cultivars Panu, Sam- po and Tammi (II) could not be given a Glu-1 quality score because they each contained a HMW glutenin subunit which has not yet been associated with bread-making quality; subunit 20 for the first two cultivars and subunit 25 for Tammi (II).The Glu-1 quality score of a cultivar can range from a minimum of 3 to a maximum of 10.For wheat varieties bred 2, Ruso; 3, Kimmo; 4, Tammi (II); 5, Hopea; 6, Ilves; 7, Aura; 8, Nisu; 9, Jyvä; 10, Linna.The region of the gel containing the HMW sub- units of glutenin is enclosed by brackets.The subunits have been numbered according to the nomenclature of Payne and Lawrence (1983).The above data includes the major biotypes only of Antti, Kiuru and Panu.   in Finland, the range is from 5 to 10 with an average of 8.0, which is very high.The 35 cultivars contain 17 different per- mutations of HMW glutenin subunits (Table 4).However, one third of the cultivars con- tain one of two HMW subunit compositions: 1,7 + 9 and 5 + 10, and 2*, 7 + 9 and 2 + 12.Only nine of the cultivars have com- positions that are unique in this collection.

Discussion
Previous studies have shown that there is a positive correlation between the Glu-1 quality score of cultivars from several Western European countries and their bread-making qualities (Payne, 1986; Payne et al. 1987).By contrast there is a negative correlation between the score and the biscuit-making quality of UK-grown wheats (Payne, et al. 1987).The Glu-1 quality score is probably therefore an indirect measure of dough strength.Finnish cultivars have the very high, average score value of 8.0.This is much higher than the mean scores of cultivars grown in the UK, West Germany(5.2and 5.8 respectively; Pay-  ne and Holt, unpublished data) and France (5.8; calculated from Branlard and Le  Blanc, 1985), but the same as the average score of cultivars grown in Australia (8.0; cal- culated from Lawrence, 1986).The cause of the high mean score value fro Finnish cultivars is probably the long tradition in this country of breeding and growing wheat primarily for conversion into bread (Kivi, 1969), whereas in the UK for example, wheats are specifically bred and grown for at least three different end uses: bread, biscuits and animal feed.
The mean Glu-1 quality score of winter wheats currently grown in agriculture in Finland is 7.8, whereas for spring wheats the aver- age score is even higher, at 8.8.There is therefore some prospect of improving the score of Finnish winter wheats in future varieties whereas one of the objectives for spring wheats should be to maintain the current, high score.
The range and distribution of HMW glutenin subunits found in Finnish-bred varieties is very limited compared to varieties grown elsewhere in Europe.Thus the chromosome 1A-encoded null allele is rare.Of the chromo- some 18-encoded subunits, subunit 7 is found only in Vakka, Ilves and Pitko and 6 + 8 only in Veka.Subunits 4+12 and 3 + 12, coded by genes on chromosome ID, are not found in any variety.The scarcity or absence of these subunits is advantageous because all of them have been associated with either mediocre or poor bread-making quality.However, if breeders in future use parental lines with greater genetic diversity than those currently used, these poor-quality subunits may be in- troduced into breeding programmes.SDS- PAGE of embryoless half-grains could then be used to advantage to screen against these subunits in subsequent generations.
Subunits 17 + 18 are not present in any of the cultivars listed in Table 2.They are coded by genes on chromosome 1B and have been associated with good bread-making quality (Payne et al. 1984).The subunits are com- mon in cultivars of Australia and Central and Southern America (Lawrence, 1986; Payne,  unpublished) and they have recently been introduced into the UK, France and Spain, in   germplasm containing reduced-height (Rht)  genes.It would be advantageous to transfer these storage-protein genes into Finnish wheats also.
The limited number of combinations of HMW glutenin subunits amongst Finnish wheats causes SDS-PAGE to be of little value in varietal identification.By contrast, alumin- ium lactate-PAGE of the gliadin proteins has been successfully used to distinguish all the varieties that are currently grown in Finland (Sontag and Salovaara, 1985), except for Ruso and Taava.However, SDS-PAGE can easily detect the presence of protein biotypes in wheat cultivars.In the very preliminary study described here, based only on the analy- sis of six grains per cultivar, three varieties were shown to be genetically mixed (Table 2).Currently the presence of storage-protein bio- types in Finnish cultivars in agriculture is being examined in much more detail.

Table 3 .
Bread-quality scores assigned to HMW sub- units of glutenin.

Table 4 .
Frequencies of various HMW glutenin subunit compositions amongst varieties.