INSTITUTE OF EXPERIMENTAL BIOLOGY AT THE ESTONIAN AGRICULTURAL UNIVERSITY
Department of Plant Genetics, 76902, Harku, Harjumaa, Estonia.
Maimu Tohver.
Success in breeding depends mostly on heritable traits and methods to identify the quality of grain in early hybrid generations. Identification of storage protein subunits is used widely in wheat-breeding programs. Prolamin gene electrophoresis is the usual method of identifying economically important characters and properties of common wheat. The HMW-glutenin subunits encoded by the Glu-1 gene are used in wheat breeding for selecting the alleles that correlate with quality.
Cultivars and breeding lines from Nordic countries are suitable for the Estonian climate and soil conditions. Many cultivars and hybrid lines are tested each year. The aim of this study was to use SDS-PAGE to identify the diversity of the glutenin proteins in hybrid lines of spring wheat originating from Scandinavia, and grown in Estonia during 2000-01. Grain stocks were obtained from the Jõgeva Plant Breeding Institute. One hundred twenty-one hybrid lines were analyzed to determine the different allelic forms of HMW glutenins. Proteins were extracted from a single kernel and electrophoresis was performed using the procedures described in D'Ovidio et al. (1996) and Tohver et al. (2001). To determine the alleles observed, the spring wheat cultivars Courtot, Chinese Spring, Marquis, and Kadett were used as standards for the HMW-glutenin subunits. The HMW-glutenin subunit banding patterns were assigned the corresponding Payne and Lawrence (1983) and UPOV (1994). Theoretical quality scores were calculated based on those assignements.
Results. A total of 13 alleles coding for 12 HMW-glutenin subunits were identified from analysis of the hybrid lines (Table 1). The greatest polymorphism was observed on chromosome 1B, with five allelic forms at the Glu-B1 locus. The most frequent alleles at the Glu-B1 locus were c, coding for subunits 7+9 (53 %, quality score (QS) 2), and b, coding for subunits 7+8 (38.6 %, QS 3). At the Glu-A1 locus, the most frequent alleles were b, coding subunit 2* (42.2 %, QS 3), and c (null allele) (40.9 %, QS 1). Allele d prevails at the Glu-D1 locus and codes for subunits 5+10 (75.6 %, QS 4). The frequent occurrence of glutenin subunits 7+8 and 7+9 encoded at the Glu-B1 locus has been reported in several European collections (Sontag-Strohm et al. 1986; Igrejas et al. 1999). We found heterogeneity in some lines with up to four different electrophoretic variants/line.
| Glu-A1 | Protein | Glu-B1 | Proteins | Glu-D1 | Proteins | |
|---|---|---|---|---|---|---|
| QS = 10 was observed in 10.8 % of cases with HMW-glutenin subunit compositions | ||||||
| b | 2* | b | 7+8 | d | 5+10 | |
| a | 1 | b | 7+8 | d | 5+10 | |
| QS = 9 was observed in 30.1 % of cases with HMW-glutenin subunit compositions | ||||||
| a | 1 | c | 7+9 | d | 5+10 | |
| b | 2* | c | 7+9 | d | 5+10 | |
| QS = 8 was observed in 24.1 % of cases with HMW-glutenin subunit compositions | ||||||
| b | 2* | b | 7+8 | a | 2+12 | |
| a | 1 | d | 6+8 | d | 5+10 | |
| c | - | b | 7+8 | d | 5+10 | |
| b | 2* | a | 7 | d | 5+10 | |
| c | - | f | 13+16 | d | 5+10 | |
| QS = 7 was observed in 22.9 % of cases with HMW-glutenin subunit composition | ||||||
| b | 2* | c | 7+9 | a | 2+12 | |
| c | - | c | 7+9 | d | 5+10 | |
| QS = 6 was observed in 12.0 % of cases with HMW-glutenin subunit composition | ||||||
| c | - | a | 7 | d | 5+10 | |
| c | - | b | 7+8 | a | 2+12 | |
The HMW-glutenin subunits influence the baking properties of wheat and triticale, but have a lesser effect in rye. Payne and Lawrence (1983) have worked out a scoring system based on HMW-glutenin subunits, and this system was used to estimate the value of breeding lines. The maximum quality score was observed 10, and the minium was 6. A large number of alleles for bread-making quality have been designated, however, only few alleles currently are in use in commercial cultivars. For that reason, novel sources of unknown alleles are needed.
From this study, we observed that breeding lines do not vary widely in HMW-glutenin subunit groups. Previously, Sontag et al. (1986) already had shown that the range and distribution of HMW-glutenin subunits found in Finnish bread wheats is very limited compared to cultivars grown elsewhere in Europe. A third of the Finnish cultivars contained one of two HMW compositions: 1, 7+9 , 5+10 or 2*, 7+9, 2+12. In Swedish wheats, the most common compositions were 2*, 6+8 or 7+9, and 2+12. Rarely have the subunits 13+16, 14+15, and 17+18 been found in Swedish wheat lines (Johansson et al. 1995). In Norwegian breeding lines, the HMW-glutenin subunit combinations 2*, 7+8, 5+10, and 2*, 13+16, 5+10 were prevalent (Uhlen 1990) and 20, 17+18 and 7 were rare subunits. From this data, the most occurring alleles in Scandinavian wheats are b at locus Glu-1A encoding subunit 2*, c at locus Glu-B1 encoding subunits 7+9, and a and d at locus Glu-D1 encoding subunits 2+12 and 5+10, respectively. Other investigators (Payne et al. 1981, 1983, 1987; Lukow et al. 1989) have shown that a positive correlation exists between high bread-making quality and the presence of the HMW-glutenin subunits 1 or 2* of Glu-A1; 7+8, 7+9, 17+18, 14+15, or 13+16 of Glu-B1, and 5+10 of Glu-D1. The low quality glutenin subunits are null of Glu-A1; 7 and 20 of Glu-B1, and 2+12 of Glu-D1. Incorporation of new subunits and their combinations could increase variation in breeding lines. Introducing the subunits 17+18 and 13+16 into Scandinavian cultivars would be necessary to widen the genetic diversity because of their correlation with good bread-making qualities.
References.