Genetic variability and analysis of screening procedures of preharvest sprouting in South African winter wheat (triticum aestivum) cultivars

English: This study classified the preharvest sprouting resistance of 17 South African winter wheat cultivars sampled over a range of typical winter wheat growth environments. Variation in sprouting response between cultivars was predominantly genetically determined and varied from 1.1 to 7.2 on a scale from 1 to 8. In general Betta-DN, Elands, Limpopo, Caledon and PAN 3235 showed good resistance to preharvest sprouting, while the hybrids Carina, Caritha and Carol, as well as the pureline Tugela-DN, tended to be highly susceptible to sprouting. Betta-DN and Elands had the best stability over environments and years. Genotypic variation appeared to be dominant, indicating that progress in the development of cultivars with sprouting tolerance is feasible. 2. In this study the oxidative pentose pathway (OPP) activity in seeds of a preharvest sprouting susceptible winter wheat cultivar, Tugela-DN and that of a preharvest sprouting resistant cultivar, Betta-DN, were compared. G6PDH activity increased twofold in both the harvest ripe (HR) and after ripened (AR) seeds of Tugela-DN during the germination phase and threefold during the post germinative phase up to 72 h of incubation. However, the G6PDH activity remained constant in both the HR and AR seeds of Betta-DN during the first 24 h of incubation and increased only slightly in the HR seeds over the remaining incubation time. Moreover, a C6/Cl ratio of below unity in seeds of Tugela-DN during the germination phase, confirmed that the OPP pathway was far more active in this preharvest sprouting susceptible cultivar than in the resistant cultivar, Betta-DN, where the C6/Cl ratio remained above unity during the germination phase. Downgrading of wheat stocks due to a low falling number is an intermittent problem in South Africa. This study determined the ability of South African winter wheat cultivars to withstand a specified amount of simulated rainfall. The falling number of cultivars that were exposed to optimal conditions for preharvest sprouting by using a rain simulator, dropped drastically in most cases. Betta-DN and Elands had a greater ability to maintain high FN during continuous rainfall than others. Limpopo, Caledon, PAN 3232 and PAN 3235 showed a high tolerance to preharvest sprouting after 72 h of simulated rain treatment, but their FN dropped to between 78s and 162s. FN determination after 72 h of rain simulation showed that visual determination could be inadequate. The G x E interactions for sprouting resistance were significant, which indicate that the more stable cultivars should be selected by breeders. 4. This study describes the findings in comparing various methods to determine preharvest sprouting and a-amylase activity. All the methods evaluated showed significant correlations and therefore any of these methods could be used for the determination of preharvest sprouting. However, results from this study indicated that the Stirring Number and Falling Number methods are the most reliable methods to use for the determination of preharvest sprouting and a-amylase activity in wheat. 5. Screening for preharvest sprouting tolerance is difficult due to the relatively low heritabi Iity of the trait and its tendency to be expressed as a quantitatively inherited character. The objectives of this study were to determine heritabi Iities and genetic variabi Iity of sprouti ng resistance in the progeny of five winter wheat cultivars, including Elands, a cultivar with excellent sprouting resistance. Five winter wheat cultivars were crossed in a complete diallel fashion to generate two sets of F1 hybrids that were used in this study. The preharvest sprouting response and a-amylase activity of these cultivars and hybrids were compared. Elands was identified as contributing positively towards preharvest sprouting tolerance in hybrid combinations. Elands also had the best overall combining ability for improvement of sprouting tolerance. 6. Preharvest sprouting resistance (i.e. high falling number values) is a major objective in the breeding programme of the ARC-Small Grain Institute. Current breeding strategies involve selection of sprouting resistant lines by using labour-intensive assessment of grain subjected to simulated rainfall. Alternative selection techniques, such as electrophoretic analysis, which require less time and grain (half a kernel per test can be used), would be desirable. The objectives of this study were to explore PAGE as a means for establishing profiles of soluble proteins of five wheat cultivars varying in their resistance to preharvest sprouting and their ensuing progeny. A protein duplet, which could possibly be associated with resistance to preharvest sprouting, was detected in five of the F2 combinations. Although the protein duplet correlated well with the preharvest sprouting scores of the cultivars and their progeny, the association is not sufficiently strong to be of practical value.