Thesis (M.Sc.Agric.) -- University of Stellenbosch, 1999. | ENGLISH ABSTRACT: Knowledge of the growth, yield and quality response of spring wheat cultivars to high temperatures is important to minimise variation that often exists in yield and breadbaking quality of wheat produced in warmer regions. To achieve this, four South African spring wheat cultivars Kariega, Palmiet, SST 55 and SST 57 were grown under controlled conditions at the University of Stellenbosch during 1998 at temperature regimes of 15/10, 20/15, 25/20 and 30/25°C during grain filling. From seeding till anthesis, plants were grown at a temperature of 15/10°C. In this study,. the highest temperature regime of 30/25°C affected all parameters tested, while at lower temperature regimes cultivars responded differently. The 30/25°C temperature regime caused premature senescence of the leaf area which was attributed to a decrease in relative leaf water content. Increased senescence of leaves at this temperature regime, reduced photosynthesis during grain filling, with the result that shriveled kernels with a lower mass kernel -1 were produced and yield plant -1 was reduced by almost 50% compared to that of the control (15/100 C). Other yield components such as kernels ear -1 were less reduced and Kariega was less affected in comparison with the other cultivars. High temperature regimes of 30/25°C during grain filling resulted in increased flour protein content. Mixogram peak heights increased as post-anthesis temperature regimes increased, while Palmiet also showed an increase in dough development time with increasing temperatures. At the highest temperature regime (30/25°C), the respective dough development times for SST 55 and SST 57 were well below the optimum mixing time of 2.5 to 3 minutes set by the baking industry, while the mixograph band widths of Kariega were the narrowest at all temperature regimes tested. This tendency indicated good water absorption properties. These results indicate that quality parameters of Kariega and Palmiet are less sensitive to high post-anthesis temperatures in comparison with SST 55 and SST 57. In general, it is concluded that although this study showed small differences between cultivars, Kariega was consistently different from other cultivars, indicating possible adaptation to hotter environments. However, more cultivars need to be screened before recommendations for such areas can be made. | AFRIKAANSE OPSOMMING: Kennis aangaande die groei-, opbrengs- en kwaliteisreaksie van lente koringcultivars teenoor hoe temperature is belangrik. Dit mag help om jaar tot variase ten opsigte van opbrengs en bakkwaliteit wat dikwels in warmer produksiegebiede voorkom, te verminder. In hierdie studie is die invloed van vier dag/nagtemperatuur-behandelings wat gedurende korrelvulling op die Suid-Afrikaanse lente koringcultivars, Karige, Palmiet, SST 55 en SST 57 toegepas is, ondersoek. Die ondersoek is gedurende 1998 onder gekontroleerde groeitoestande by die Universiteit van Stellenbosch uitgevoer. Vanaf planttyd tot antese is aile plante gegroei by 'n dag/nagtemperature van 15/10oC. Vanaf antese tot oes is die kontrole plante steeds aan hierdie temperatuur blootgestel, terwyl die ander plante aan dag/nagtemperature van onderskeidelik 20/15°C, 25/200C en 30/25°C blootgestel is. In hierdie studie is aile gemete eienskappe deur die hoogste dag/nag tempertaure beinvloed en het cultivars nie grooteliks verskil in hul reaksie nie. Verskille in cultivarreaksie het wei by die laer dag/nagtemperature voorgekom. Die 30/25°C temperatuurbehandeling het blaarafsterwing versnel weens 'n verlaging in die relatiewe water inhoud van die blare. Dit het blaaroppervlakte-duurte en dus ook fotosintese gedurende korrelvulling benadeel met die gevolg dat verkrimpte, maer korrels geproduseer en opbrengs plant-1, in vergelyking--met die kontrole plante, met byna 50% verlaag is. Ander opbrengskomponente soos korrels aar -1 is minder ernstig benadeel en Kariega was ietwat meer tolerant as die ander cultivars. Hoe dag/nagtemperatuurgedurende korrelvulling het tot 'n toename in meelproteieninhoud aanleiding gegee. Mixogram-piekhoogtes het ook toegeneem met toenemende temperature. In teenstelling met ander cultivars het Palmiet ook 'n toename in deegontwikkelingstyd getoon. By die hoogste dag/nagtemperatuur (30/25°C) was deegontwikkelingstye van die cultivars SST 55 en SST 57 betekenisvol laer as die optimum tye van 2.5 - 3.0 minute wat deur die bakbedryf vereis word. Waardes vir Kariega was meer aanvaarbaar en mixogram bandbreedtes vir kariega was ook by aile temperatuurbehandelings die smalste. Dit is 'n aanduiding van goeie waterabsorpsie-einskappe. Hierdie resultate toon dat die bakkwaliteit van Kariega en Palmiet minder gevoelig is vir hoe temperature gedurende korrlevulling in vergelyking met SST 55 en SST 57. In hierdie studie is gevind dat hoewel verskille in cultivareaksie oor die algemeen klein was, Kariega ietwat beter aanpassing by die hoe temperature getoon het. Meer cultivars sal egter getoets moet word alvorens aanbevelings in die warmer produksiegebiede gemaak kan word. | Master

From the obtained results we can note that the parasitoids in our experiments in 1 997 and 1998 had considerable influence on decline of aphids population density, at which the percent of parasitization in milk maturity stage of wheat was from 2.7 to 35%. The culmination of parasitization was recorded in our experiments about 7-10 days after the culmination of population density of aphids. The obtained results did not confirm the definite influence of different growing systems on parasitization of aphids, because in 1997 the parasitization was very high in integrated growing system and in 1998 in ecological growing system. The influence of different growing systems on aphids parasitization appeared during a given year and within an growing system. It also appeared between different years and it was found that these differences were significant. The parasitoids found were: Aphidius ervi Haliday, A. rlwpalosiphi De Stefani-Pcrcz, A. uzbekistanicus Luzhctzki, Praon volucre (Hal iday), Ephedrus plagialor (Nees), Diaeretiefla rapae (M'lntosh). In 1997, the most abundant species were Aphidius ervi and A. rhopafosiphi and in 1998 A. ubekistanicus and Aphidius ervi.

In 1995-1998, the frequency of selected virulences in the powdery mildew ( Blumeria graminis f. sp. tritici ) population on wheat in the Czech Republic was investigated. Samples of conidia were collected by a mobile version of a spore-trap. A total of 1739 one-colony isolates were analysed on a set of five varieties as differentials. High frequencies (> 50%) were found for virulences Vm2, Vm3a, Vm5 and Vml7, lower frequencies(< 50%) for combinations Vm9,2,1 and Vm2,6 and for Vm4b. There were no significant changes in virulence frequencies except for genes Vm5 and Vm9,2,1 that showed one-year variations. Differences between the eastern part (Moravia) and western part (Bohemia) of the Czech Republic were mostly insignificant for most exam­ ined genes. A significantly higher virulence frequency was found in Moravia for genes Vm3a (in 1995) and Vml7 (in 1996), and in Bohemia for the combination Vm9,2,1 (in 1995). A significant correlation (tested by Kendall's tau B values) existed between Vm2 and Vm5 in 1997 and 1998, and between Vm4b and Vm5 in 1995 and 1998. Values of gametic disequilibrium were also studied. Changes in the complexity of isolate virulence were determined to be small and showed no definite trend.

Wheat (Triticum aestivum L.) yield is limited by wheat streak mosaic virus which is vectored by the wheat curl mite (WCM) Aceria tosicheilla (Keifer). Host resistance to WCM has reduced losses. This study was conducted to evaluate the effectiveness of resistance in wheat to WCM collected from various locations in the Great Plains. Collections of WCM from Montana, Nebraska, South Dakota, Texas, Alberta, Canada, and eight locations in Kansas were compared for their ability to survive and reproduce in the greenhouse on seven lines of wheat and wheat relatives previously identified as resistant. The lines and their sources of resistance were: AC PGR16635 (Aegilops tauschii Coss., Cmc1), PI525452 (Thinopyrum ponticum (Podp.) Liu and Wang, Cmc2), KS96WGRC40 (Ae. tauschii and Secale cereale L.), TA920 (Triticum timopheevii (Zhuk.) Zhuk spp. armenidcum), PI 475772 (S. cereale), 'TAM 107' (S. cereale), PI 222655 (T. aestivum). KS96WGRC40 and TA920 were the only entries that were resistant to all WCM collections. Other sources of resistance were effective against WCMs from some but not all locations. PI 222655 was resistant to WCMs from Nebraska and central Kansas but not to mites from most other locations. WCMs that were virulent to TAM 107 generally were also virulent to PIs 222655 and 475772 but avirulent to Cmc2. The WCMs from western Kansas, where TAM 107 is widely grown, were generally more virulent to that cultivar than WCM from central Kansas where the hectarage of TAM 107 is smaller. WCMs collected at different times or locations may vary in their responses to different sources of resistance; therefore, testing mites for their response to resistance genes advanced in breeding programs may be needed before resistant cultivars are deployed in the field.

The nature of the interprotein interactions in wheat gluten is discussed with particular reference to the role of the high molecular weight subunits. It is argued that the high molecular weight subunits interact with each other by disulphide bonds and hydrogen bonds. Dough working favours the formation of end to end disulphide bonds in the subunits and this increases the effective molecular weight of the subunit and hence the number of protein-protein interactions. Association of the subunits can also take place by interchain hydrogen bonding. So many hydrogen bonds are formed that not all can be broken simultaneously although there will be unbonded mobile regions (loops) and bonded regions (trains). Stretching extends loops and then causes the proteins to slide over one another. The elastic restoring force is provided by the re-establishment of the loop train equilibrium.

Objective: Wheat fiber appears to protect from cardiovascular disease despite its lack of consistent effect on serum lipids. We therefore wished to determine whether reported inconsistencies in the effect of wheat bran resulted from differences in particle size or its high gluten content. Methods: Two studies were conducted. In one-month metabolic diets, 24 hyperlipidemic subjects consumed breads providing an additional 19 g/d dietary fiber as medium or ultra-fine wheat bran and extra protein (10% of energy as wheat gluten). In two-week ad libitum diets, 24 predominantly normolipidemic subjects consumed breakfast cereals providing an additional 19 g/d of dietary fiber as coarse or a mixture of ultra-fine and coarse wheat bran with no change in gluten intake. Both studies followed a randomized crossover design with control periods when subjects ate low-fiber breads and cereals respectively with no added gluten. Fasting blood lipids were measured on day zero and at the end of each phase. Results: Wheat bran had no effect on total, LDL or HDL cholesterol irrespective of particle size or level of gluten in the diet. However, consumption of increased gluten in the metabolic study was associated with a 13 +/- 4% reduction in serum triglycerides (p = 0.005) which was not seen in the normal-gluten ad libitum study. Conclusions: The protective effect of wheat fiber in cardiovascular disease cannot be explained by an effect of wheat bran in reducing serum cholesterol although in hyperlipidemic subjects displacement of carbohydrate by gluten on the high-fiber phases was associated with lower serum triglycerides.