Identification of genetic variation in bread wheat quality characteristics in the Western Cape

English: 1. The objective of this study was to select environmentally stable parental lines, and to determine the heritability of quality characteristics, the correlation between these characteristics, the combining ability of these quality characteristics, and the selection response. 2. A parental trial was planted at two diverse environments namely langgewens and Tygerhoek, to determine the influence of environment on the different quality traits and parents. locality had a significant influence on most of the characteristics (FPC, EX, FCL, MDT, FA, LFV, BSI,TKM and yield) whereas HlM, FSTand FOT were not influenced by the environment. 3. A correlation matrix performed on the collected data from the two localities showed that correlations tend to be environment specific. There were no consistent correlations between characteristics across envi ronments. 4. As expected, locality had a significant influence on most of the quality characteristics. Parents should be selected on average performance across localities. Kariega, SST 57 and Palmiet showed the least interaction with the environment and should therefore be considered as parents. Gamtoos was the best parent for FA and FST, but because of the 1B/1R translocation's negative effect on quality, this cultivar should be avoided as a parental line to improve quality. 5. At langgewens a diallel trial was conducted, on the parents and the F2 progeny, to determine the correlations, heritability, combining ability and selection response of the different quality characteristics. 6. Significant effects were found over the four replications for some of the quality characteristics. From this trial, Palmiet, Kariega, Nantes and SST57 were found to perform very well. Nantes and Kariega were involved in almost all the best performing F2 combinations and even though the progeny was F2, some heterosis was stiII evident. 7. Significant GCA was found for all the traits except FN, FCL and SDS. SCA was significant for FN, HLM and LFV, which could be an indication of heterotic effects in these traits. 8. To produce the best progeny, parental lines with the highest GCA for a specific trait should be used. High GCA effects is an indication of additive gene action, which again indicates high heritability. Kariega, Nantes, SST 57 and Palmiet proved to be the best cultivars to improve the different quality and yield characteristics. 9. The best specific combination to produce progeny with desirable milling characteristics was Nts/Kar, whereas Kar/Gmt proved to be the best specific combination to improve the rheological characteristics simultaneously. W92- 1/Nts can be used to develop desirable progenies for LFV. SST57/Kar proved to be the best combination to improve TKM. The SCA of W92-1 proved to be mostly influenced by the environment. 10. The GCA:SCA ratio was calculated to determine whether a character shows more additive or non-additive gene action. The following characteristics showed additive gene action: TKM, EX, BFY, FCL, HLM, GPC, LFV, MDT and FPC. The remainder of the characteristics showed very little variation between additive and non-additive gene action, except for FN, where the SCA was much higher. 11. To further confirm the above findings, the additive gene action was determined. Results were in agreement with previous findings, stating that TKM, EX and BFY was mainly under additive control, FCL, HLM, GPC, LFV, MDT and FPC showed mainly additive but also non-additive gene action and FN and SDS were under non-additive genetic control. 12. A phenotypic correlation matrix was performed to determine whether a positive or negative correlation exists between the quality and yield characteristics. Significant positive correlations were observed between HLM and TKM, EX and MDT, GPC and LFV and FPC, SDS and LFV, BFY and LFV, EX and MDT, FPC and LFV and FCL and MDT. This implies that selecting for one of these traits will simultaneously improve the other traits in a desirable environment. None of these correlations correlated with findings in the parental trial. Significant negative correlation existed between TKM and GPC and EX and FCL, implying a selection for one trait will influence the other trait negatively. 13. A genetic correlation matrix was also performed. Significant positive genetic correlations were observed between SDS and FN (0.858*), MDT and HLM (0.815*) and LFV and FPC (0.824*) indicating that an increase in one of these characteristics will result in an increase of the other character as well, irrespective of the environment. In the phenotypic correlation matrix these correlations were positive as well, but non-significant. 14. The broad and narrow sense heritability was calculated for the quality and yield characteristics. The narrow sense heritability varied from as high as 0.7089 for TKM to 0 for SDS and FN. These findings again indicate a good success in selecting for higher TKM. The broad sense heritabilities were relatively high for most of the characters, indicating a significant environmental influence in the non-additive or heterotic effects of these genes. 15.lndirect selection was calculated to find out whether it is possible to achieve more rapid progress through selection for a correlated response than from selection for the desired character itself. None of the indirect selections showed high response to selection for TKM and GPC, therefore to improve these characters, selection should be applied directly. Direct selection would be better to improve FCL, because of the negative correlations with the characteristics. None of the indirect selected characters could improve all the other characters simultaneously, but selection for HLM and MDT improved all the characteristics except FCL. Direct selection procedures should rather be used to improve specific quality characteristics. Indirect selection would be best to select for SDS and FN.