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

[摘要] English: This study classified the preharvest sprouting resistance of 17 South Africanwinter wheat cultivars sampled over a range of typical winter wheat growthenvironments. Variation in sprouting response between cultivars waspredominantly genetically determined and varied from 1.1 to 7.2 on a scalefrom 1 to 8. In general Betta-DN, Elands, Limpopo, Caledon and PAN 3235showed good resistance to preharvest sprouting, while the hybrids Carina,Caritha and Carol, as well as the pureline Tugela-DN, tended to be highlysusceptible to sprouting. Betta-DN and Elands had the best stability overenvironments and years. Genotypic variation appeared to be dominant,indicating that progress in the development of cultivars with sproutingtolerance is feasible.2. In this study the oxidative pentose pathway (OPP) activity in seeds of apreharvest sprouting susceptible winter wheat cultivar, Tugela-DN and that ofa preharvest sprouting resistant cultivar, Betta-DN, were compared. G6PDHactivity increased twofold in both the harvest ripe (HR) and after ripened (AR)seeds of Tugela-DN during the germination phase and threefold during thepost germinative phase up to 72 h of incubation. However, the G6PDHactivity remained constant in both the HR and AR seeds of Betta-DN duringthe first 24 h of incubation and increased only slightly in the HR seeds overthe remaining incubation time. Moreover, a C6/Cl ratio of below unity inseeds of Tugela-DN during the germination phase, confirmed that the OPPpathway was far more active in this preharvest sprouting susceptible cultivarthan in the resistant cultivar, Betta-DN, where the C6/Cl ratio remainedabove unity during the germination phase.Downgrading of wheat stocks due to a low falling number is an intermittentproblem in South Africa. This study determined the ability of South Africanwinter wheat cultivars to withstand a specified amount of simulated rainfall.The falling number of cultivars that were exposed to optimal conditions forpreharvest sprouting by using a rain simulator, dropped drastically in mostcases. Betta-DN and Elands had a greater ability to maintain high FN duringcontinuous rainfall than others. Limpopo, Caledon, PAN 3232 and PAN 3235showed a high tolerance to preharvest sprouting after 72 h of simulated raintreatment, but their FN dropped to between 78s and 162s. FN determinationafter 72 h of rain simulation showed that visual determination could beinadequate. 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 determinepreharvest sprouting and a-amylase activity. All the methods evaluatedshowed significant correlations and therefore any of these methods could beused for the determination of preharvest sprouting. However, results from thisstudy indicated that the Stirring Number and Falling Number methods are themost reliable methods to use for the determination of preharvest sproutingand a-amylase activity in wheat.5. Screening for preharvest sprouting tolerance is difficult due to the relativelylow heritabi Iity of the trait and its tendency to be expressed as a quantitativelyinherited character. The objectives of this study were to determineheritabi Iities and genetic variabi Iity of sprouti ng resistance in the progeny offive winter wheat cultivars, including Elands, a cultivar with excellentsprouting resistance. Five winter wheat cultivars were crossed in a completediallel fashion to generate two sets of F1 hybrids that were used in this study.The preharvest sprouting response and a-amylase activity of these cultivarsand hybrids were compared. Elands was identified as contributing positivelytowards preharvest sprouting tolerance in hybrid combinations. Elands alsohad the best overall combining ability for improvement of sprouting tolerance.6. Preharvest sprouting resistance (i.e. high falling number values) is a majorobjective in the breeding programme of the ARC-Small Grain Institute.Current breeding strategies involve selection of sprouting resistant lines byusing labour-intensive assessment of grain subjected to simulated rainfall.Alternative selection techniques, such as electrophoretic analysis, whichrequire less time and grain (half a kernel per test can be used), would bedesirable. The objectives of this study were to explore PAGE as a means forestablishing profiles of soluble proteins of five wheat cultivars varying in theirresistance to preharvest sprouting and their ensuing progeny. A proteinduplet, which could possibly be associated with resistance to preharvestsprouting, was detected in five of the F2 combinations. Although the proteinduplet correlated well with the preharvest sprouting scores of the cultivars andtheir progeny, the association is not sufficiently strong to be of practical value.

[发布机构] University of the Free State