Bibliography: leaves 131-153. This thesis investigates the mechanisms of manganese (Mn) efficiency (genetic tolerance to Mn-deficient soils) in barley (Hordeum vulgare L.) at both physiological and molecular levels.

Bibliography: leaves 173-200 / iv, 200 leaves, 7 leaves of plates : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, 1986

Bibliography: leaves 121-141. / viii, 151 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Plant Science, 1996?

Bibliography: leaves 131-153. / xiii, 153 leaves : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / This thesis investigates the mechanisms of manganese (Mn) efficiency (genetic tolerance to Mn-deficient soils) in barley (Hordeum vulgare L.) at both physiological and molecular levels. / Thesis (Ph.D.)--University of Adelaide, Dept. of Plant Science, 1996

Cereal crop productivity is hampered when these plants are infested by phloem feeding aphids. A great deal of research has been carried out with the direct aim of a clearer understanding of the mechanism involved in the interaction between aphids and their host plants. Research has directly or indirectly been geared towards enhanced plant productivity and achieving sustainable agriculture. Barley (Hordeum vulgare L.) is an important small grain crop in South Africa, whose crop performance is negatively affected by fluctuations in weather patterns as well as by agricultural pests. One of the insect pests infesting barley is the Russian wheat aphid, Diuraphis noxia Kurdjumov (RWA), of which the two South African biotypes, codenamed RWASA1 and RWASA2, were studied in this thesis. During dry spells, RWA infestation becomes a more serious threat to barley productivity. Resistant plants have been used to combat RWA infestation of small grains. In South Africa, 27 RWA-resistant wheat cultivars are currently used in commercial cultivation, but no resistant barley lines have, unfortunately, been developed, in spite of this grain’s significant economic importance. This informed the study in this thesis, and this interest particularly focussed on three RWA-resistant lines developed by the USDA, testing their performance against South African RWA biotypes, for possible adaptation to South Africa. The aim was thus to examine the plant-aphid interactions, aphid breeding rates, plant damage and sustainability, evidence of resistance or tolerance and finally potential performance under elevated CO2 (a very real climate change threat). Two major avenues of research were undertaken. The first aspect involved examination of structural and functional damage caused by RWASA1 and RWASA2 on the three resistant and a non-resistant line. Aphid population growth and damage symptoms (chlorosis and leaf roll) of infestation by these aphid biotypes were evaluated. This was followed by a structural and functional approach in which the effects of feeding on the transport systems (phloem and xylem) of barley were investigated. Fluorescence microscopy techniques (using aniline blue fluorochrome, a specific stain for callose and 5,6-CFDA, a phloem-mobile probe) were applied to investigate the feeding-related damage caused by the aphids, through an examination of wound callose formation and related to this, the resultant reduction in phloem transport capacity. Transmission electron microscopy (TEM) techniques provided evidence of the extent of the feeding-related cell damage. The second aspect involved a study of the effect of changing CO2 concentrations ([CO2]) on the resistant and susceptible barley cultivars to feeding by the two RWA biotypes. Leaves of plants grown at ambient and two elevated levels of [CO2] were analysed to investigate the effect of changing [CO2] on biomass, leaf nitrogen content and C:N ratio of control (uninfested) and infested plants. The population growth studies showed that the populations of the two RWA biotypes as well as bird cherry-oat aphid (BCA, Rhopalosiphum padi L.) increased substantially on the four barley lines. BCA was included here, as it had been the subject of several previous studies. RWASA2 bred faster than RWASA1 on all lines. The breeding rates of the two RWA biotypes were both suppressed and at near-equivalent levels on the three resistant lines, compared to the non-resistant PUMA. This suggests that the resistant lines possessed an antibiosis resistance mechanism against the feeding aphids. Feeding by the aphids manifested in morphological damage symptoms of chlorosis and leaf roll. The two biotypes inflicted severe chlorosis and leaf roll on the non-resistant PUMA. In the resistant plants, leaf rolling was more severe because of RWASA2 feeding compared to RWASA1 feeding. In contrast, chlorosis symptoms were more severe during RWASA1 feeding than was the case with RWASA2 feeding. Investigation of the effect of aphid feeding on the plants showed that callose was deposited within 24h and that this increased with longer feeding exposure. Wound callose distribution is more extensive in the non-resistant PUMA than in the resistant plants. RWASA2 feeding on the resistant lines caused deposition of more callose than was evident with RWASA1 feeding. During long-term feeding, it was evident that variation in the intensity and amount of wound callose was visible in the longitudinal and transverse veins of the resistant plants. Of the three STARS plants, STARS-9301B had the least callose. Interestingly, wound callose occurred in both resistant and non-resistant plants, in sharp contrast to what has been reported on resistant wheat cultivars that were developed in South Africa. The relative reduction in the wound callose deposited in the resistant line, when compared to the non-resistant lines, suggests the presence of a mechanism in the resistant lines, which may prevent excessive callose formation. Alternatively, the mechanism may stimulate callose breakdown. RWASA2 feeding on the resistant lines deposited more wound callose than RWASA1 feeding. This evidence supports the hypothesis that RWASA2 is a resistance breaking and more aggressive feeder than RWASA1 is; and further underscores the urgent need for development of RWA-resistant barley cultivars. The ultrastructural investigation of the feeding damage showed that the two biotypes caused extensive vascular damage in non-resistant plants. There was extensive and severe cell disruption and often obliteration of cell structure of the vascular parenchyma, xylem and phloem elements. In sharp contrast, among the resistant plants, feeding-related cell damage appeared to be substantially reduced compared to the non-resistant PUMA. Low frequency of damaged cells indicated that majority of the cell components of the vascular tissues were intact and presumed functional. There was evidence of salivary material lining the secondary walls of the vascular tissue, which resulted in severe damage. Within xylem vessels, saliva material impregnated half-bordered pit pairs between the vessels and adjacent xylem parenchyma. This is believed to prevent solute exchange through this interface, thereby inducing leaf stress and vi leaf roll. A notable finding is that RWASA2 effectively induced more cell damage to vascular tissues in the resistant lines than did RWASA1. In general the experimental evidence (see Chapter 5) suggests that the resistant lines are possibly more tolerant (or able to cope with) to RWA feeding. Evidence for this is the reduction of wound callose and at the TEM level, a comparatively less obvious cell damage in the resistant lines, which suggests that they possess antibiosis and tolerance capacity. The apparent reduction of feeding-related cell damage from the TEM study confirmed the disruptive action of the feeding aphids in experiments using the phloem-mobile probe, 5,6-CF. Results showed that feeding by RWASA1 and RWASA2 reducedthe transport functionality of the phloem in all cases, but that RWASA2 feeding caused a more obvious reduction in the rate and distance that 5,6-carboxyfluorescein was transported, than did RWASA1. Investigation of the effect of changing [CO2] on the barley cultivars showed that in the absence of aphids and under elevated CO2 conditions, the plants grew more vigorously. In this series of experiments, the infested plants suffered significant reduction in biomass under ambient (as was expected) and under the two elevated CO2 regimes. Biomass loss was greater at elevated CO2 than under ambient [CO2]. The infested nonresistant PUMA plants showed a more significant biomass loss than did the resistant cultivars. Clearly, the benefits derived from elevated CO2 enrichment was thus redirected to the now-advantaged aphids. Uninfested vii plants showed an increase in leaf nitrogen under the experimental conditions. However, feeding aphids depleted leaf nitrogen content and this was more apparent on plants exposed to RWASA2 than was the case with RWASA1. The end result of this was that C:N ratio of infested plants were higher than uninfested plants. Clearly, the faster breeding rates of the aphids at elevated CO2 caused depletion of N and a resultant deficiency exacerbated chlorosis as well as leaf rolling due to the higher aphid population density under elevated CO2 than at ambient. By 28 days after infestation (DAI), majority of the plants exposed to enriched CO2 treatments had died. A major finding here was thus that although this study demonstrated that elevated CO2 resulted in an increase in biomass, this was detrimentally offset in plants infested by the aphids, with a decline in biomass and loss of functionality leading to plant death at 28DAI. The overriding conclusion from this study is a clear signal that the twin effects of CO2 enrichment (a feature of current climate change) and aphid infestations may precipitate potential grain shortages. A disastrous food security threat looms.

This study involves a measure of the variability of descendants from a cross between Ustilago hordei race 7 and race 11, on two varieties of barley, Trebi and Odessa. Components of variability were defined, statistically described and compared. Biometrical analyses uncovered the action of significant additive and non-additive genetic effects. Differential interactions between treatments and varieties revealed the existence of at least one virulence gene. Specific polygenes and the virulence gene were found to produce significant interactions with different environmental conditions. Homogeneity of variance of the genetic components of the F2 from three randomly chosen F1 dikaryotic lines demonstrated the highly homozygous condition of the parental teliospores. Covariance - variance regression analysis was used to study the dominance and epistatic differences between treatment dikaryons. There is evidence for ambidirectional dominance. The number of effective factors operating against the varieties, Trebi and Odessa, were estimated to be between 4-6 and 1-2 respectively. / Science, Faculty of / Botany, Department of / Graduate

Common barley diseases observed in North Dakota include net blotch, spot blotch, leaf and stripe rust, bacterial leaf streak, and Fusarium head blight. The first objective of this research was to determine the effect of variety and fungicide timing on disease development of barley under conventionally tilled systems. Five field trials were performed in 2016-2017 to test the effect of common varieties and fungicide applications on foliar disease of barley. Overall, varietal selection had a greater effect on the level of foliar disease observed than fungicide application. The second objective focused on the efficacy and timing of adepidyn and prothioconazole + tebuconazole on Fusarium head blight. An inoculated greenhouse experiment was performed the fall of 2017 to determine the effectiveness of fungicide timing at half-spike, full-spike, and five days after full-spike. The protectant capabilities of the fungicides were greater than their curative properties.

Please read the abstract in the section 00front of this document / Dissertation (MSc (Genetics))--University of Pretoria, 2002. / Genetics / unrestricted

Thesis (PhD)--Stellenbosch University, 2015 / ENGLISH ABSTRACT : Diuraphis noxia Kurdjumov (Russian Wheat Aphid; RWA) is a pest of wheat and barley that has spread from its home range in the fertile crescent to most wheat producing countries except Australia. Since its first introduction to South Africa and the USA in the late 20th century, breeding programs for wheat phenotypes resistant to the aphid were put in place. Conventional breeding practices rely on phenotypic screening to verify traits carried by offspring and genetic tools such as marker assisted selection (MAS) have greatly aided this process in speed and accuracy. The size and complexity of the wheat genome, its allopolyploid nature and repetitive elements have, however, posed a challenge to studies on the genetics of this cereal crop. Many studies have focused on chromosome 3B which is the largest of the wheat chromosomes and easily separated from the redundant genomic background by techniques such as flow cytometry. The similarity in size of the remaining chromosomes however, limits the application of flow cytometry to their isolation. Databases such as Grain-Genes (http://wheat.pw.usda.gov/GG2/index.shtml) house marker data from various mapping studies for all wheat chromosomes and in 2014 the International Wheat Genome Sequencing Consortium (IWGSC) completed the draft genome sequence of wheat categorized by chromosome. Sources of resistance (Dn resistance genes) against RWA are located on chromosome 7D. but despite the marker and sequence data available currently, mapping studies specific for the Dn resistance genes are few. Additionally, sequence data available is derived from cultivars susceptible to RWA and is not comprehensively annotated and assembled in many cases. In this study, we demonstrate a novel, combined approach to isolate and characterize the Dn resistance genes through the use of a genetic map constructed from Amplified Fragment Length Polymorphism (AFLP), Expressed Sequence Tag (EST) and microsatellite markers and a physical map constructed from Next Generation Sequencing (NGS) data of ditelosomic chromosomes (7DS and 7DL) isolated by microdissection on the PALM microbeam system. A 122.8 cM genetic map was produced from 38 polymorphic AFLP markers and two ESTs with the microsatellite Xgwm111 as anchor to related genetic maps. Through comparison to maps available on GrainGenes the location of the Dn1 resistance gene was narrowed down to a deletion bin (7DS5-0.36-0.62) on the short arm of chromosome 7D with an AFLP marker (E-ACT/M-CTG_0270.84) mapping closely at 3.5 cM and two ESTs mapping at 15.3 cM and 15.9 cM from Dn1. Isolation of individual chromosome arms 7DS and 7DL using the PALM Microbeam system allowed sequencing of the chromosome without the redundancy of the remainder of the hexaploid genome. Through isolating the chromosome arms in this way, a >80-fold reduction in genome size was achieved as well as a major reduction in repetitive elements. Analysis of the sequencing data confirmed that 7DL is the physically shorter arm of the chromosome though it contains the majority of protein coding sequences. / AFRIKAANSE OPSOMMING : Diuraphis noxia Kurdjumov (Russiese koring-luis; RWA) is « pes wat op koring en gars voorkom. Die pes het vanaf sy tuiste in die midde Ooste na meeste koringproduserende lande behalwe Australië versprei. Sedert die eerste bekendstelling van RWA in Suid Afrika en die VSA in die vroeë 20ste eeu is teelprogramme ten gunste van koring lyne met weerstand teen RWA begin. Tradisionele teelprogramme maak op fisieise observasie van die fenotipe staat om te verifieer of plante in die nageslag die gewenste eienskap dra. Genetiese metodes soos merkerondersteunde seleksie (MAS) versnel hierdie selekteringsproses grootliks. Die grootte en kompleksiteit van die koring genoom asook die polyploïde en herhalende natuur daarvan is « groot hindernis vir genetiese studies van hierdie graangewas. Baie studies het op chromosoom 3B gefokus wat die grootste van die koring chromosome is en dus maklik vanaf die res van die oorbodige genomiese agtergond deur tegnieke soos vloeisitometrie geskei word. Die ooreenkoms in grootte tussen die res van die chromosome bemoeilik die toepassing van vloeisitometrie om hulle te isoleer. Databasisse soos GrainGenes (http://wheat.pw.usda.gov/GG2/index.shtml) bevat merker data vanaf verskeie karterings-studies vir al die chromosome en in 2014 het die "International Wheat Genome Sequencing Consortium"(IWGSC) die voorlopige basispaarvolgorde van die koring genoom bekendgestel, gekategoriseer volgens chromosoom. Weerstandsbronne (Dn weerstandsgene) teen RWA kom meestal op chromosoom 7D voor. Ten spyte van merker en basispaarvolgorde data tans beskikbaar is karterings-studies spesifiek tot die Dn gene skaars en basispaarvolgorde data is vanaf kultivars afkomstig wat nie weerstandbiedend teen RWA is nie en waarvan die annotasie en samestelling baie keer nie goed is nie. In hierdie studie demonstreer ons « nuwe, gekombineerde aanslag om die Dn weerstandsgene te isoleer en karakteriseer deur van « genetiese kaart opgestel met "Amplified Fragment Length Polymorphism"(AFLP), "Expressed Sequence Tag"(EST) en mikrosatelliet merkers asook « fisiese kaart saamgestel deur die volgende-generasiebasispaarvolgordebepaling van ditelosomiese chromosome (7DS en 7DL) geïsoleer deur mikrodisseksie met die "PALM Microbeam"sisteem gebruik te maak. « Genetiese kaart van 122.8 cM was met 38 polimorfiese AFLP merkers en twee EST merkers geskep. Die mikrosatelliet, Xgwm111, is ook ingesluit en het as anker vir verwante genetiese-kaarte gedien. Deur vergelyking met genetiese-kaarte op GrainGenes is die posisie van die Dn1 weerstandsgeen vernou na « delesie bin (7DS5-0.36-0.62) op die kort arm van chromosoom 7D met « AFLP merker (EACT/ M-CTG_0270.84) wat ongeveer 3.5 cM vanaf die geen karteer. Die twee EST merkers is 15.3 cM en 15.9 cM vanaf die geen gekarteer. Isolering van die individuele chromosoom arms, 7DS en 7DL, deur van die "PALM Microbeam"sisteem gebruik te maak het basispaarvolgordebepaling van die chromosoom toegelaat sonder die oortolligheid van die res van die hexaploïde genoom. Deur die chromosoom so te isoleer is « >80-maal verkleining in genoom grootte bereik insluitend « groot reduksie in herhalende elemente. Analise van die data vanaf basispaarvolgordebepaling het bevestig dat chromosoom 7D die fisiese kleiner chromosoom is maar dat dit die meerderheid van proteïn koderende basispaarvolgordes bevat.

Please read the abstract in the section 00front of this document / Dissertation (MSc (Agric) Plant Pathology)--University of Pretoria, 2003. / Microbiology and Plant Pathology / unrestricted