Thesis (PhD (Agric) (Conservation Ecology and Entomology))--University of Stellenbosch, 2005. / Six tortricid species are of major economic importance to the South African fruit industry. They are the codling moth Cydia pomonella, the oriental fruit moth Grapholita molesta, the false codling moth Thaumatotibia leucotreta, the macadamia nut borer T. batrachopa, the litchi moth Cryptophlebia peltastica and the carnation worm Epichoristodes acerbella. For phytosanitary purposes and to aid the management of population levels of the aforementioned species, their identities at species and population level were investigated using morphological and molecular genetic techniques. Morphological characteristics were used to distinguish and differentiate between the final instar larvae and pupae of the six species. For this purpose the morphology of the final instar larvae and pupae of the Afrotropical species T. leucotreta, T. batrachopa, Cr. peltastica and E. acerbella was described and illustrated using line drawings and scanning electron micrographs. Taxonomic characters found to be useful for the identification of the larvae were the presence and structure of the anal comb and the number and arrangement of crochets on the prolegs. The pupae could be distinguished based on the presence or absence of a distinct cremaster, the shape of the spiracle, the position of the setae on the anal rise, the structure of the mouthparts and the length of the procoxa in relation to that of the protarsus. These characters were used to develop keys to distinguish between the tortricid species occurring on tropical and subtropical fruit (T. leucotreta, T. batrachopa and Cr. peltastica) and deciduous fruit (E. acerbella, C. pomonella, G. molesta and T. leucotreta). At population level, molecular techniques were employed to compare geographic populations of each of the six species. Amplified fragment length polymorphism (AFLP) analysis with five selective primer pairs was used to investigate genetic diversity. In addition, host populations of species were compared where relevant. No evidence was found to suggest that populations from different hosts were genetically differentiated. However, geographic populations were found to be genetically distinct in each of the six species, with extensive genetic divergence apparent over local geographic scales and significantly high estimates of population differentiation ranging between Gst = 0.2625 and 0.3778. Factors influencing the genetic population structure of the six species were investigated by comparing the amount and distribution of genetic variation between oligophagous and polyphagous species as well as introduced and native species. Results indicated that host range and population history did not have a major effect on population genetic structure. It was therefore suggested that other factors such as limited dispersal were responsible for the extensive genetic divergence observed between geographic populations of each of the six tortricid species. These results should be incorporated into existing pest management programs and taken into consideration when designing new control strategies. This is the first report of its kind to identify, with a high level of accuracy, the aforementioned tortricids and the first to determine the population genetic structure of these species.

Dissertation (PhD)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: A survey was conducted in the Western Cape Province during the 1999/2000 and 2000/2001 seasons on mealybugs occurring in vineyards. P/anococcus ficus (Signoret) was the dominant mealybug in vineyards during this time. During this study P. ficus was recorded for the first time on roots of grapevines, which has far reaching implications for the control of this important vine leafroll virus vector as control actions were focused on above ground control. Other mealybugs presently recorded in local vineyards included Pseudococcus /ongispinus (Targioni) and Ferrisia ma/vastra (McDaniel). Pseudococcus viburni (Maskell) and Ps. so/ani Ferris were found on weeds in vineyards. Natural enemies of P. ficus recorded most frequently were species of Nephus predatory beetles, and the parasitaids Coccidoxenoides peregrinus (Timberlake), Anagyrus sp. and Leptomastix dacty/opii (Howard). Developmental studies on P. ficus and C. peregrinus indicated that the intrinsic rate of increase (rm) was similar, peaking at 25°C (rm = 0.169 for P. ficus; rm = 0.149 for C. peregrinus). The net replacement rate (Ra) was higher for P. ficus than for C. peregrinus at all five temperatures tested. The Ra for P. ficus reached a maximum at 21°C (308.87) and C. peregrinus at 25°C for C. peregrinus (69.94). The lower and upper thresholds for development of P. ficus were estimated at 16.59 and 35.61°C respectively. The lower threshold for development of C. peregrinus was 8.85°C. These parameters indicated that both insects were well adapted to temperatures in the Western Cape Province. The lower minimum threshold temperature of C. peregrinus in relation to that of P. ficus suggests that C. peregrinus should be more active during winter and early spring than P. ficus. A central systematic presence-absence sampling system was developed for P. ficus. Monitoring three different plant parts on the vine indicated that new growth areas on vines adjacent to the main stem could serve as an early warning system for pending P. ficus bunch infestations. Intervention should be planned when 2 % of the stems are infested with P. ficus when using this system. Seasonal population studies of P. ficus and its natural enemies showed that stem infestation by P. ficus reached peak levels during January in Robertson and Stellenbosch and during February in the Hex River Valley. Vine mealybugs colonised new growth early in the season, followed by the leaves and eventually the bunches towards the end of the season. High stem infestations early in the season resulted in high bunch infestation levels at harvest. A density dependent relationship was evident between P. ficus populations and parasitoid populations, suggesting that the parasitoids played a mayor role in the biological control of P. ficus populations. Biological control was however only achieved towards the end of the season when damage to the crop had already occurred. Mass releases of C. peregrinus on P. ficus populations were done in order to augment biological control as an alternative to chemical control. Between five and six releases of 20 000 C. peregrinus per release were done at monthly intervals in three grapegrowing areas. Mass released C. peregrinus controlled P. ficus adequately in the Hex River Valley. Control of P. ficus using this approach was no worse than using chemical control in Robertson and Stellenbosch. C. peregrinus is commercially available and can therefore be used as an alternative to chemical control by producers. Degree day estimation was used to predict development of P. ficus populations. This information was used as an input in a P. ficus pest management model. Data acquired from P. ficus and ant monitoring were used as components to construct a decision chart. This chart can be used by producers to optimise the control of P. ficus populations using either chemical control or mass releases of C. peregrinus. / AFRIKAANSE OPSOMMING: "n Studie is gedurende die 1999/2000 en 2000/2001 seisoene gedoen met die doelom die witluisspesies wat in wingerde voorkom, te identifiseer. Planococcus ficus (Signoret) is tans die dominante witluisspesie in wingerde in die Wes Kaap Provinsie. P. ficus kolonies is op wingerdwortels gevind. Dié bevinding kan verreikende gevolge hê vir die beheer van dié plaag as "n belangrike rolbladvirus vektor aangesien beheer tot dusver gefokus het op bogrondse gedeeltes. Ander witluisspesies wat in wingerde gevind is, sluit in Pseudococcus /ongispinus (Targioni) en Ferrisia malvastra (McDaniel). Pseudococcus vibumi (Maskell) en Ps. so/ani Ferris is op onkruide in wingerde gevind. Dominante natuurlike vyande van P. ficus sluit predatoriese kewertjies van verskeie Nephus spp. en die parasitoïede Coccidoxenoides peregrinus (Timberlake), Anagyrus sp. en Leptomastix dacty/opii (Howard) in. Ontwikkelingstudies op P. ficus en C. peregrinus het aangetoon dat die inhirente voortplantingstempo (rm) soortgelyk was vir beide insekte met "n maksimum by 25°C (0.169 vir P. ficus, 0.149 vir C. peregrinus). Die netto vervangingstempo (Ra) was in vergelyking met C. peregrinus hoër vir P. ficus by al vyf temperature getoets. Die Ra van P. ficus het "n maksimum bereik teen 21°C (308.87) en die van e. peregrinus by 25°C (69.94). Die teoretiese hoër en laer drempels vir ontwikkeling van P. ficus was onderskeidelik 16.59 en 35.61 oe. Die teoretiese laer drempelwaarde van ontwikkeling vir e. peregrinus was 8.85°e. Hierdie parameters dui aan dat beide insekte goed aangepas is by temperature in die Wes Kaap Provinsie. Die laer minimum drempel vir ontwikkeling van C. peregrinus in verhouding tot P. ficus impliseer dat C. peregrinus in die winter en vroeë lente meer aktief sal wees as P. ficus. 'n Sentrale sistematiese aan-afwesig moniteringsisteem met bekende vlakke van steekproefnemingsfout is ontwikkel in kommersiële wingerde vir P. ficus. Monitering van drie verskillende dele op die wingerdstok het aangedui dat die nuwe groei areas kan dien as 'n vroeë waarskuwing vir latere P. ficus trosinfestasies. Dié sisteem sal produsente in staat stelom te bepaal wanneer optrede noodsaaklik is. Daar word voorgestel dat optrede noodsaaklik is by 'n P. ficus besmettingsvlak van 2 % op die nuwe groei areas op stokke. Stambesmetting deur P. ficus het in Januarie piekvlakke bereik in Stellenbosch en Robertson, en in Februarie in die Hex Rivier Vallei. P. ficus koloniseer nuwe groei vroeg in die seisoen waarna blare en trosse aan die einde van die seisoen gekoloniseer word. Dié data dui aan dat P. ficus besmetting op nuwe groei vroeg in die seisoen 'n aanduiding kan gee van hoë trosbesmetting aan die einde van die seisoen. 'n Digtheidsafhanklike verwantskap was waarneembaar tussen P. ficus plaagpopulasies en parasitoïed populasies. Dié verwantskap dui aan dat parasitoïede die belangrikste rol speel in biologiese beheer van P. ficus populasies. Biologiese beheer van witluis is egter eers aan die einde van die seisoen bereik toe die oes reeds beskadig was. Massavrylatings van C. peregrinus is in P. ficus besmette blokke gedoen om biologiese beheer aan te help en sodoende as alternatief tot chemiese beheer te dien. Tussen vyf en ses vrylatings met 20 000 C. peregrinus is een keer per maand gedurende die seisoen gedoen. Die vrygelate C. peregrinus het P. ficus populasies voldoende beheer in die Hex Rivier Vallei. Beheer van P. ficus deur massavrylatings van C. peregrinus was soortgelyk as chemiese beheer in Robertson en Stellenbosch. C. peregrinus is kommersieel beskikbaar en kan om hierdie rede as alternatief tot chemiese beheer gebruik word. Graaddag bepaling is gebruik om die ontwikkeling van P. ficus populasies te voorspel. Hierdie inligting is gebruik as 'n verdere hulpmiddel in die P. ficus plaagbeheermodel. Inligting verkry vanuit P. ficus en mier monitering is gebruik as komponente in die opstel van 'n besluitnemingstabel. Hierdie tabel kan gebruik word deur produsente om beheer van P. ficus plaagpopulasies te optimaliseer deur chemiese beheer of massavrylatings van C. peregrinus.

Thesis (PhD (Agric))--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: During a survey in the greater Cape Flats Heterodera schachtii was found to be widespread on cauliflower, Brussels sprouts, beetroot and cabbage. The numbers present were above two eggs and juveniles per gram of soil, generally regarded as the economic threshhold level of infestation and requiring control. The damage potential of H schachtii on vegetables, as well as the ability of certain weeds to serve as a source of infection on subsequent crop plantings was studied under greenhouse conditions and resulted in a reduction of yield and root weight of crops. Population densities of H schachtii increased significantly under favourable hosts like cabbage where densities of 198 eggs and juveniles per gram of soil were reached. The most commonly occurring weeds maintained nematode development and increased their population densities. They can thus serve as alternative hosts in the absence of susceptible hosts and should be routinely controlled. The life cycle and biology of H schachtii was also studied. Penetration of plant tissue and subsequent development on vegetables, weeds and trap crops were observed. Penetration was successful on all crops tested reaching 37% and 52% at inoculum levels of 22 and 11 juveniles per gram of soil, respectively. Subsequent development of H schachtii on weeds and vegetables was similar, but in the case of cauliflower and black nightshade as hosts, their life cycle was shorter in comparison to other crops. The possible existence of varying susceptibility of crops to different populations of H schachtii was examined by comparing the rates of penetration in crops and reproduction of geographically isolated populations of H schachtii in the greater Cape Flats. When root penetration, virulence and juvenile emergence were examined, populations from Lynedoch and Philippi were distinct from the other populations. Subsequently, representative individuals of these populations were subjected to PCR-RFLP, but with these techniques real differences between the various populations could not be adequately detected. The environmental parameters such as soil texture, temperature and pH on H schachtii were investigated as to their influence on the root weight and yield of crops. Reductions in the yield of beetroot and cabbage were observed with soil temperatures ranging between 15 to 30°C. Migration and penetration of H schachtii juveniles declined with an increase in clay and silt content of the soil. Above a 34% silt and clay content of soil, no migration and penetration took place. Root penetration levels of 30% and higher were reached with pH varying between 4.5 and 7.4. This resulted in a significant reduction in yield of crops. Crop rotation is an essential component of non-chemical control. In the case of H schachtii, it required one host crop in four non-host rotational cycles to maintain the population of the nematode in the soilless than three eggs and juveniles per gram of soil. The inclusion of a trap crop reduced the population densities to below two eggs and juveniles per gram of soil. It therefore also forms an integral part of a control strategy. Solarization proved successful as a physical control method. Best results were obtained in summer with clear polyethylene which led to a 97% reduction of infective juveniles. This method can be applied during the late summer in the greater Cape Flats, just before the onset of winter. This may safeguard future spring plantings. The need for effective control strategies in order to reduce the numbers of H schachtii is of the utmost importance to ensure vegetable production in the future. Small-scale farmers should therefore be educated in this respect. / AFRIKAANSE OPSOMMING: Heterodera schachtii het wydverspreid in 'n opname in die groter Kaapse Vlakte voorgekom op beet, blomkool, Brusselse spruite en kopkool. Die nematode getalle by alle lokaliteite was bo die algemeen aanvaarbare ekonomiese drempelwaarde van twee eiers en larwes per gram grond wat beheer regverdig. Die skadepotensiaal van H schachtii op groente, sowel as die vermoë van sekere onkruide om as infeksie bronne te dien vir opvolgende gewasse, is in glashuise ondersoek en het tot 'n verlaging in opbrengs en wortelmassa by gashere gelei. Die populasie digthede van H schachtii het met die aanplant van geskikte gashere tot vlakke van 198 eiers en larvae per gram grond gestyg. Die mees algemeen voorkomende gasheeronkruide het nematode ontwikkeling in stand gehou en selfs tot 'n populasie verhoging gelei. Hierdie onkruide is 'n beperkende faktor vir die verbouing van groente aangesien die onkruide as alternatiewe gasheer kan dien in die afwesigheid van gashere en onkruidbeheer moet dus op 'n gereelde basis toegepas word. Die lewenssiklus en biologie van H schachtii is ondersoek deurdat die penetrasie van gasheer wortels en die daaropvolgende ontwikkeling op groente, onkruide en vanggewasse vergelyk is. Penetrasie, vyf dae na inokulasie, is met alle gashere verkry met 37% en 52% penetrasie met inokulum vlakke van 22 en 11 larwes per gram grond onderskeidelik. Daaropvolgende ontwikkeling van H schachtii was soortgelyk op groente en onkruide, maar blomkool en nastergal het as gashere 'n verkorte lewenssiklus tot gevolg gehad. Die moontlikheid van verskille in die virulensie van H schachtii is ondersoek deur die penetrasie van gewasse en reproduksie vlakke van nematodes van nege verskillende geografies geskeide populasies in the groter Kaapse Vlakte te vergelyk. Die Lynedoch en Philippi populasies het onderskeibare resultate gelewer ten opsigte van die populasies uit die ander lokaliteite, maar geen verskille kon met PKR-RFLP aangetoon word nie. Die invloed van omgewings parameters, grondtekstuur, temperatuur en pH, is op H schachtii ondersoek ten opsigte van opbrengste en wortelmassa van gewasse. Grondtemperature tussen 15°C - 30°C het tot die grootste daling in opbrengs gelei op kopkool en beet. Migrasie en penetrasie het afgeneem met 'n toename in klei en slik inhoud tot en met 'n klei en slik inhoud van 34%, waarna geen penetrasie en migrasie voorgekom het nie. Wortelpenetrasie van 30% en hoër het voorgekom by pH vlakke van tussen 4.5 - 7.4 met die gepaardgaande verlaging in opbrengs van gewasse. Afwisseling van gewasse is 'n essensiële metode van nie-chemiese beheer van nematode getalle in die grond. Die mees optimale rotasie ten opsigte van H schachtii beheer is met die aanplanting van een gasheer gewas in vier gewas aanplantings verkry. Die insluiting van 'n vanggewas in die gewas rotasie siklus het die nematode populasievlakke tot onder twee per gram grond laat daal. Solarisasie is suksesvol uitgevoer met deurskynende poli-etileen in die groter Kaapse Vlakte gedurende die somer met gevolglik 'n 97% vermindering van die getalle infektiewe nematodes. Effektiewe beheermaatreëls ten opsigte van H schachtii moet in die groter Kaapse Vlakte ingestel word om groente-produksie in hierdie gebied te verseker. Kleinboere moet in hierdie tegnieke opgelei word.

Thesis (MSc)--Stellenbosch University, 2000. / Full text to be digitised and attached to bibliographic record. / ENGLISH ABSTRACT: The cultivation of citrus in the Vaalharts region is a fairly recent development. With the introduction of this crop, an insect pest complex has also developed in this region. The presence of these pests was studied in eleven orchards, planted with three citrus cultivars and of varying ages, distributed in the 300 square kilometer cultivation area. Each orchard was inspected for the presence of pests by making use of two weekly sampling techniques. Ten of the most important insect pests of citrus in the Vaalharts region are briefly described by refering to their general appearance, life cycles, feeding and pest status and economic threshold. For every pest various control options, including operational systems, crop cultivation, biological and chemical control, are discussed and, where applicable, illustrated by means of graphic presentations. The seasonal presence of the cirtrus pests in the Vaalharts region is tabulated and discussed individually. With these details as background, an insect pest management programme for citrus in the Vaalharts region is compiled. / AFRIKAANSE OPSOMMING: Die verbouing van sitrus in die Vaalhartsgebied is 'n redelik onlangse ontwikkeling. Gepaard met die nuwe gewas het daar ook 'n insekplaagkompleks in die gebied ontstaan. Die voorkoms van die plae is in elt .boorde, beplant met drie sitruskultivars en van verskillende ouderdomme, verspreid in die 300 vierkante kilometer verbouingsareaal, bestudeer. Elk van die boorde is weekliks ondersoek vir die aanwesigheid van plae deur van twee moniteringstegnieke gebruik te maak. Die tien belangrikste insekplae van sitrus in die Vaalhartsgebied word kortliks beskryf deur na hulle algemene voorkoms, lewenssiklus, voeding en plaagstatus en ekonomiese drempelwaardes asook die moniteringsmetodes wat gebruik is, te verwys. Vir elke plaag word beheeropsies, wat operasionele stelsels, gewasverbouing, bloloqlese en chemiese beheer insluit, bespreek wat, waar toepaslik, aan die hand van grafiese voorstellings gemustreer word. Die seisoenale aanwesigheid van die sitrusplae word in 'n tabel aangedui en individueel bespreek. Met die gegewens as agtergrond is 'n insekplaagbestuurprogram vir sitrus in die Vaalhartsgebied opgestel.

Striga, a genus of obligate parasitic weeds in the family Orobanchaceae, has been identified as the most important biological factor limiting agricultural productivity in sub-Saharan Africa. Germination of Striga seeds is triggered by strigolactone root exudates from host plants. Strigolactones also induce hyphal branching in arbuscular mycorrhizal (AM) fungi, which are important for plant uptake of phosphorus in low phosphorus soils. Mechanisms of Striga resistance based on reduced strigolactone production may also convey resistance to AM fungi which would require higher inputs of phosphorus fertilizer to attain optimal crop growth. There is evidence for genetic differences in mycorrhizal responsiveness in other grain crops; therefore it is beneficial for breeders to be aware of these differences when developing Striga-resistant sorghum cultivars. This research aims to determine phosphorus and mycorrhizal responsiveness of sorghum genotypes important for or developed by breeders working on Striga resistance. Phosphorus response curves were determined for twelve sorghum genotypes using pasteurized low phosphorus soil amended to achieve four different phosphorus levels. Simple linear regression was performed on root and shoot dry weight data. Results indicate variability in phosphorus responsiveness within Striga resistant and susceptible genotypes. Seven of these genotypes were selected for continued research, which analyzed responsiveness to phosphorous and differences in mycorrhizal responsiveness in relation to reported mechanisms of Striga resistance. Treatments included three levels of phosphorus amendments and the addition of Funneliformis mosseae inoculum. All genotypes were strongly responsive to P amendment when grown without AM fungi and showed a decrease in responsiveness to P when inoculated with F. mosseae. Trends for all genotypes indicate a greater uptake of P, Zn, and Mg by mycorrhizal plants as compared to nonmycorrhizal plants. All seven genotypes were responsive to mycorrhizae, with a significant increase in biomass for all genotypes, especially at the lowest phosphorus level. The responsiveness to the mycorrhizal fungus does not appear to be directly related to the susceptibility of genotypes to the parasitic weed Striga. / Graduation date: 2012

This dissertation describes two different projects. The first is the development of an oral DNA vaccine delivery system for fish. A novel oral DNA vaccine delivery system was developed for Rainbow Trout by combining non-viral vectors (polycationic liposomes or polycationic polymer) to facilitate the DNA vaccine's uptake by cell membranes along with enteric-coated protection of the DNA embedded in microparticles to prevent DNA degradation in the gastrointestinal tract. Spray drying and spray coating bead techniques were employed in the preparation of the DNA vaccine microparticles. The spray drying technique allowed production of spherical shape enteric-coated microparticles with a particle size range of 0.18 to 20 ��m. Larger particle sizes of 40-50 mesh were obtained from the spray-coated bead technique. The resultant DNA vaccine microparticles were granulated with regular fish feed and given to fish to investigate the efficacy of the delivery system in providing protection against IHNV, and to demonstrate the ease of administration in fish. An in vivo fish trial experiment showed improvement in fish survival rate when fish were immunized with larger particle size DNA vaccine microparticles. Further research to find effective vector carriers for the DNA vaccine delivery system and to seek modifications of the delivery system that will still prevent the denaturation of plasmid DNA that will also facilitate membrane uptake of the DNA vaccine is needed in order to develop a safe, effective, and commercially viable vaccine to control the outbreak of IHNV. The second project of the dissertation is prediction of in vitro drug release profiles from a novel matrix tablet spray-coated with a barrier membrane using mathematical and statistical models. Tablets were prepared by direct compression followed by spray coating. The relationship of the amount of hydrophilic materials in the core tablets and barrier thickness on drug release mechanism was investigated using factorial design and regression analysis. Drug release characteristics were influenced and can be controlled by modifying the amount of hydrophilic materials in the core tablet and the barrier thickness. Mathematical equation generated from regression analysis of n-value, lag time, and percent drug release as a function of the amount of hydrophilic material and the amount of coating material applied can now be used as a tool for predicting and optimizing in vitro drug release from matrix tablets spray-coated with a barrier membrane. / Graduation date: 2003

The objective of this study was to characterize an unknown agent associated with decline in black raspberry (Rubus occidentalis) in Oregon. A virus was found consistently associated with decline symptoms of black raspberries and was named Black raspberry decline associated virus (BRDaV). Double stranded RNA extraction from BRDaV-infected black raspberry revealed the presence of two bands of approximately 8.5 and 7 kilobase pairs, which were cloned and sequenced. The complete nucleotide sequences of RNA 1 and RNA 2 are 7581 nt and 6364 nt, respectively, excluding the 3' poly(A) tails. The genome structure was identical to that of Strawberry mottle virus (SMoV), with the putative polyproteins being less than 50% identical to that of SMoV and other related sequenced viruses. The final 189 amino acids of the RNA-dependent- RNA-polymerase (RdRp) reveal an unusual indel with homology to AlkB-like protein domains, suggesting a role in repair of alkylation damage. This is the first report of a virus outside the Flexiviridae and ampeloviruses of the Closteroviridae to contain these domains. An RT-PCR test was designed for the detection of BRDaV from Rubus tissue. BRDaV is vectored non-persistently by the large raspberry aphid Amphorophora agathonica, the green peach aphid Myzus persicae, and likely nonspecifically by other aphid species. Phylogenetic analysis of conserved motifs of the RdRp, helicase, and protease regions indicate that BRDaV belongs to the Sadwavirus genus. To assess the rate of spread BRDaV, four newly planted fields of black raspberries (Rubus occidentalis) in Oregon were studied for three years. In an effort to characterize the suspected complexity of synergistic interactions between BRDaV and other Rubus-infecting viruses, the prevalence of ten additional Rubus viruses was also monitored in the study fields. The timing of BRDaV infection as it relates to aphid populations and flights was also determined. Testing of nearby vegetation identified several symptomless Rubus hosts of BRDaV, as well as detection in multiple cultivars of black raspberry and several non-Rubus weeds. It was determined that BRDaV spreads rapidly with a low aphid threshold and consistently is associated with decline of black raspberries in Oregon. / Graduation date: 2006

Maize (Zea mays L.) streak virus disease (MSD) is the most important virus disease in Africa but farmers are unaware of its status. A project was initiated to assess the current status of MSD and to breed for its resistance. Four populations comprised of two BC1F1 and two F2 progenies developed by backcrossing and selfing the F1 progenies of two crosses between a donor line (CMl 202) and two susceptible lines (CMl 321 and CMl 384) were developed. Conventional and molecular marker assisted selection (MAS) methods were used to screen for resistance to MSD in each of the four populations. To facilitate unbiased comparison, separate screening nurseries were established for MAS and conventional screening. The objectives of the study were five-fold; 1) to assess the status of MSD in Uganda and understand farmers' preferences and varietal selection criteria for maize using a participatory rural appraisal (PRA), 2) to screen for MSD resistance in early generations of segregating maize populations using conventional method, 3) to screen for resistance to MSD using SSR marker assisted selection , 4) to compare the effectiveness of marker assisted selection and conventional methods for selection for resistance to MSD, and 5) to compare costs associated with MAS and conventional selection methods. Results of PRA showed that unreliable rainfall and insect pests were the dominant constraints to maize productivity in Uganda. Diseases were ranked fifth among the production constraints . Maize streak virus disease was considered the most important disease constraint. Farmers showed common preference for high yielding and early maturing cultivars. However, farmers had other special preferences which were diverse and included large, white and high test density kernels for marketing, and sweet taste, particularly for home consumption. Farmers' research priorities included tolerance to drought, resistance to insect pests and diseases, sweetness, prolificacy, resistance to lodging, and drooping leaves because theyt cover the soil fast and prevent weed growth. Conventional screening for resistance to MSD showed that backcross and selfing populations segregated in 1:1 and 3:1 Mendelian ratios confirming the presence of one major gene with simple inheritance . Severity and incidence of disease were positively correlated suggesting a non-reference by the insects. In the selfing populations, the presence of complete esistance against MSD was suggested because frequency distribution patterns were highly skewed in favour of resistance. There was a decrease in disease severities with selection from BC1F1 to BC2F1 and from F2 to F3 generations indicating that high response to selection was achieved. On the other hand, one marker, umc1917, consistently polymorphic and eo-dominant was selected and used in MAS protocol. Results showed that the observed outcomes fitted the expected ratio of 1:2:1 for a F2 population and 1:1 for a BC1F1 population (X2 not significant). Evaluation of F3 and BC2F1 progeny selected using markers showed low disease severity suggesting that marker assisted selection was effective. However, the study showed that the presence of the O'Tl, was not consistent with symptom expression in the field. Evaluation of lines in three-way crosses identified ten potential lines that were high yielding, highly resistant to MSD and stable across three locations. Both MAS and conventional selection were equally effective in identifying high yielding lines although resistance was higher under MAS. Costs of MAS and conventional method varied depending on the units for comparison. The total costs of conventional method were higher than that of MAS in both first and second selection cycles. Comparing costs per row for conventional and costs per plant or data point for MAS showed that conventional selection was 2.4 times more expensive than costs per sample for MAS. However, costs per plant for MAS were 6.6 times higher than for conventional selection. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2006

Soybean rust (SBR) caused by Phakopsora pachyrhizi Syd. is an aggressive wind dispersed fungal disease which has spread around the world at an alarming rate in the last decade. The disease was first reported in South Africa (SA) in 2001. It has become well established in the province of KwaZulu-Natal. Reports are occasionally made from eastern Mpumalanga, late in the growing season, in years with good rainfall. Yield losses of 10 - 80% have been reported due to SBR infection. Literature was reviewed to better understand the pathogen in an attempt to find suitable disease management strategies. Many strategies involve delaying, rather than preventing, SBR infection. Of the two strategies to prevent infection, the use of fungicides was the only option for disease control in SA, as no resistant cultivars are available. Field trials were conducted to determine which fungicides are effective in controlling SBR. Further research was conducted to determine the timing, frequency and rate of fungicide applications for optimal control of SBR. Trials were evaluated for disease severity, seed yield and the effect of fungicides on seed quality. Fungicides from the triazole class of the sterol biosynthesis inhibiting group of fungicides were found to be the most effective in controlling SBR. A fungicide from the strobilurin group was found to be less effective than the triazoles at the suggested rate, but was found to be as effective when evaluated at higher dosage rates. Triazoles premixed with fungicides from the benzimidazole and strobilurin groups were also effective in controlling SBR. Timing of application was found to be critical for strobilurin fungicides, but not for triazole fungicides, which have a curative ability, unlike strobilurins. Strobilurin fungicides applied preventatively, before the appearance of disease symptoms were as effective as triazole fungicides applied after disease symptoms, but before infection levels had reached 10%. Across both wet and dry seasons two fungicide applications applied at 21d intervals at the R2 growth stage resulted in effective disease control. In wet seasons, a third fungicide application resulted in yields that were higher, albeit not statistically significant, than two fungicide applications. Assessments of individual fungicides for optimal dosage rate found that registered rates were already optimal for some fungicides, but for others it appeared as if alterations were necessary to the rate suggested for registration. This study was one of the first to extensively evaluate the efficacy of the new triazole and strobilurin fungicides on SBR control. The results have been shared globally, but particularly with newly affected countries in South and North America. Although this research has been groundbreaking, there are still many aspects of fungicide control which need to be studied in order to further optimise chemical control of SBR. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2005

Five potential resistance-inducing chemicals were applied to two sugarcane varieties (N12 and N27) in a pot trial with the aim of inducing resistance to nematodes in naturally-infested soil. BION® (acibenzolar-S-methyl), methyl jasmonate, cis-jasmone and 2,6-dichloroisonicotinic acid (INA) were applied as a foliar spray and suSCon® maxi (imidacloprid) applied to the soil. All chemicals were tested at two rates and plants were sprayed one week prior to being harvested at 7, 9 and 11 weeks of age. Meloidogyne and Pratylenchus infestation of sett and shoot roots was determined at each harvest. The activity of four pathogenesis-related proteins was examined at 7, 9 and 11 weeks using separate assays, these enzymes where chitinase, β-1,3-glucanase, peroxidase and polyphenol oxidase. Methyl jasmonate treatment produced significant increases in β-1,3-glucanase, chitinase and peroxidase activity. All other elicitor treatments showed little difference in enzyme activity from the Control. The effect of each treatment on plant growth was examined by recording the dried root and shoot biomass of each plant. No significant differences were seen (p<0.05; Holm-Sidak test). However, root and shoot dried biomass was highest in the N12 variety treated by suSCon® maxi. The infection of sugarcane with Ustilago scitaminea (sugarcane smut) is commonly identified visually by the presence of a smut whip. Identification of sugarcane smut infection can be determined prior to whip development by staining tissue sections with lactophenol cotton blue and examining plant tissues microscopically. This allows for a rapid determination of smut infection which can aid breeding programs. Smut infection is achieved in vitro by soaking sugarcane setts in smut spores collected from infected whips. Four methods of inoculation were examined. The method that most consistently caused infection involved allowing setts to germinate for 24 hours, before puncturing a bud with a toothpick, followed by submerging the sett in 1x10⁸ smut spores per mℓ. An elicitor of systemic acquired resistance called BION®, and an insecticide with resistance-inducing properties called Gaucho® (imidacloprid) were used as a sett soak treatments to induce resistance to sugarcane smut. The effect of each treatment at three concentrations on plant germination and growth was examined in the NCo376 variety. Smut spore germination on agar was examined in the presence of both treatments at three concentrations. Sugarcane setts were treated with a concentration that did not significantly reduce the germination of smut spores or sugarcane setts. Plants were infected with smut post treatment and allowed to grow for approximately one month until plants were between 8 and 10 cm in height. Smut infection was assessed by cutting longitudinal sections through the base of the shoot and staining each section with cotton blue lactophenol. Treatment with BION® and Gaucho® did not reduce smut infection. / M.Sc.Agric. University of KwaZulu-Natal, Pietermaritzburg 2013.