The inheritance and genetic expression of low molecular weight glutenin subunits in South African wheat cultivars

English: 1. The aim of this study was to identify: a) The HMW glutenin subunit composition in South African bread and durum wheats. b) The effectiveness of LMW glutenins for the identification of bread and durum wheat varieties. c) Different classes of LMW glutenins. d) The differences in the band intensities of the different classes. e) The correlations between the certain combinations. f) The genetic distances between cultivars in bread and durum varieties. g) A new LMW glutenin nomenclature system that can help to distinguish between bread wheat cultivars. 2. The cultivars were screened in a gliadin-free background using a simplified onedimensional procedure of Singh et al (1991). The HMWand LMW glutenins were run on a single gel. 3. The results were as follows: a) Many cultivars had the same HMW banding combinations in bread and durum wheats. It was therefore not possible to use HMW glutenins to distinguish between cultivars. b) The LMW glutenins were, however, very effective to distinguish between cultivars. It was also possible to distinguish between cultivars with a close genetic relationship and between near isogenic lines. c) Thirty-nine different classes of LMW glutenins were determined with the help of the standard deviations of different cultivars. d) It was possible to assign different band intensities to different classes. Some classes contained light bands, while other contained dark bands. There were also bands of medium intensity. In some classes light and dark bands occured in the replications of the same cultivar. e) Correlations were found between certain combinations. f) The genetic distances between cultivars showed that there are genetic variation between durum wheat varieties, but that some bread wheat varieties are very closely related. g) A new nomenclature system was identified and this proved to be sufficient to distinguish between the different cultivars. 4. The conclusions of this study are: a) The HMW glutenins must not be used for cultivar identification in South Africa. It is only reliable to determine seed purity before commercialising new varieties. b) The LMW glutenins are very effective to distinguish between cultivars. c) The new nomenclature system is very effective for cultivar identification. It explains more of the variation between cultivars than the nomenclature system of Gupta and Shepherd (1990). d) Using this system, genetic markers must be identified for bread-making quality. It must also be tested if certain bands alone are responsible for bread-making quality and if combinations of bands determine a good bread wheat cultivar. e) The influence on quality of the intensities of bands in the different classes must also be tested.