Thesis (MScAgric)--Stellenbosch University, 1956. / ENGLISH ABSTRACT: no abstract available / AFRIKAANSE OPSOMMING: geen opsomming

Thesis (MSc)--University of Stellenbosch, 2007. / ENGLISH ABSTRACT: Presently, the observed variation in symptoms of Potato leafroll virus (PLRV) infection in potato cultivars in South Africa cannot be reconciled with PLRV symptoms obtained 10-15 years ago, even if the different interactions between the pathogen and the cultivar are taken into account. In an effort to analyze this variation, mutations in the coat protein (CP) gene of South African isolates of PLRV were assessed. The CP gene of PLRV isolates from different areas within South Africa was amplified by reverse transcription-polymerase chain reaction (RT-PCR), cloned and sequenced. Significant sequence variation in the CP gene was found within the analyzed South African isolates of PLRV. Phylogenetic analysis revealed two major clades with most South African isolates and an Australian and North American isolate grouped together and the remainder grouped with isolates from diverse countries worldwide. The deduced amino acid sequences from representatives of these two clades indicated differences in CP threedimensional structure. In an effort to produce recombinant PLRV CP for the production of antibodies specific for South African isolates of PLRV for use in enzyme-linked immunosorbent assay (ELISA), the CP gene of a South African isolate of PLRV was subcloned into a bacterial expression vector (pET14-b). Expression of full length recombinant PLRV CP was attempted in Escherichia coli strains BL21(DE3)pLysS, Rosetta-gami B(DE3)pLysS and Rosetta-2(DE3)pLysS. As this was not successful, the PLRV CP gene was subcloned in another expression vector (pGEX) for expression as an N-terminal fusion protein with glutathione-S-transferase (GST) in E. coli strains BL21(DE3)pLysS and Rosetta-2(DE3)pLysS. The recombinant GST-PLRV CP fusion protein was purified and used for antibody production in rabbits. Using western blots, the effectiveness of antibodies produced to recombinant GST-PLRV CP fusion protein was assessed for PLRV recognition. It was found that antibodies to the recombinant GST-PLRV CP fusion protein were more effective for the detection of GST than PLRV CP and that production of antibodies to the cleaved PLRV CP product would be necessary if antibodies are required for ELISA applications. / AFRIKAANSE OPSOMMING: Huidiglik kan die waargeneemde simptome van infeksie met aartappelrolbladvirus (Potato leafroll virus, PLRV) in aartappelkultivars in Suid-Afrika nie vereenselwig word met PLRV simptome wat 10-15 jaar gelede verkry was nie, selfs al word die verskillende interaksies tussen die patogeen en kultivar in ag geneem. In ‘n poging om hierdie variasie te analiseer, was mutasies in die mantelproteïen (CP) geen van Suid-Afrikaanse isolate van PLRV bepaal. Die CP geen van PLRV isolate van verskillende areas in Suid-Afrika was ge-amplifiseer met behulp van die tru transkripsie-polimerase ketting reaksie (RT-PCR), gekloneer en die nukleotiedvolgorde bepaal. Noemenswaardige nukleotied variasie is in die CP gene van die ge-analiseerde Suid-Afrikaanse isolate van PLRV gevind. Filogenetiese analises het gedui op twee hoof klades met die meeste van die Suid-Afrikaanse isolate wat saam met ‘n Australiese en Noord-Amerikaanse isolaat gegroepeer en die res wat met isolate van verskillende lande wêreldwyd gegroepeer. Die afgeleide aminosuurvolgordes van verteenwoordigers van bogenoemde twee klades het gedui op verskille in die CP driedimensionele struktuur. In ‘n poging om rekombinante PLRV CP te produseer vir die produksie van antiliggame spesifiek teen Suid-Afrikaanse isolate van PLRV om in “enzyme-linked immunosorbent assay” (ELISA) te gebruik, was die CP geen van ‘n Suid-Afrikaanse isolaat van PLRV gesubkloneer in ‘n bakteriële ekspressie vektor (pET14-b). Daar was gepoog om vollengte rekombinante PLRV CP in die Escherichia coli rasse BL21(DE3)pLysS, Rosetta-gami B(DE3)pLysS en Rosetta- 2(DE3)pLysS te produseer. Aangesien dit nie suksesvol was nie, was die PLRV CP gesubkloneer in ‘n ander ekspressie vektor (pGEX) sodat die proteïen as ‘n N-terminale fusie proteïen met “glutathione-S-transferase” (GST) in E. coli rasse BL21(DE3)pLysS en Rosetta- 2(DE3)pLysS geproduseer kon word. Die rekombinante GST-PLRV CP fusie proteïen was gesuiwer en gebruik vir antiliggaam produksie in konyne. Die effektiwiteit van die antiliggame wat teen rekombinante GST-PLRV CP fusie proteïen geproduseer was vir PLRV herkenning is deur middel van “western blots” geanaliseer. Dit was gevind dat antiliggame teen die rekombinante GST-PLRV CP fusie proteïen meer effektief was vir die herkenning van GST as PLRV CP. Gevolglik sal dit nodig wees om antiliggame teen die gesnyde PLRV CP produk te maak vir gebruik in ELISA.

Thesis (MSc)--Stellenbosch University, 1981. / ENGLISH ABSTRACT: No abstract available / AFRIKAANSE OPSOMMING: Die aard, omvang en beheer van voelskade by wyndruiwe is ondersoek in die streek Stellenbosch - Simonsberg. Die Mossie (Passer melanurus, Willer) en die Europese spreeu (Sturnus vulgaris, Linnaeus) veroorsaak die meeste voelskade aan.wyndruiwe in die streek. Die kultivars gebruik in die ondersoek Was Chenin blanc, Pint noir, Riesling, Cinsaut, Clairette blanche en Cabernet Sauvignon. Die laagste suiker- en tic.ogsbasuurgehaltes waarby voelskade voorgehom het was onderskeidelik 11,2° Balling en 25,9g per l,- terwyl vreetskade by gemiddelde 12,4°. Balling en 19,1 g per l totale suur begin het. Die belangrikste enkele faktor wat t rol gespeel het by beskadiging was die suikerkonsentrasie. Die patroon van vreetskade oor t wingerdry is bepaal en het getoon dat die eerste 30 stokke aan weerskante van die wingerd die meeste beskadig word. 'n Metode is vasgestel cm die hoeveelheid skade aangerig te bepaal met behulp van tellings van beskadigde korrels in verteenwoordigende wingerdrye. Die skade in die streek is op 2,5% van die totale opbrengs per hektaar bepaal. Die bespuiting van wingerdblokke en alternatiewe buffer-kantrye met die afskrikmiddel metiokarb (Mesurol) teen 'n konsentrasie van 0,1% or genoemde kultivars, asook Muskadel, het onvoldoende beheer gebied. Bespuitings teen hoer konsentrasies word aanbeveel.

Dissertation (PhD (Agric))--University of Stellenbosch, 2000. / ENGLISH ABSTRACT: A study was made of the basic biology of subterranean Eriosoma lanigerum (Hausmann) populations in apple orchards in the Western Cape Province of South Africa. The absence of cornicles and the presence of a vulva could be used to identify 1st instar nymphs and adults respectively. Body length, body width and length of the hind femur are useful for separating 2nd , 3rd and 4th instars. However, separation of 2nd from 3rd instar nymphs was very unreliable. Maximum population growth rate was at 23°C while at 30 °C population growth was zero. The estimated minimum and maximum threshold temperatures for development were 4.32 and more than 30°C respectively. Numbers of underground E. lanigerum in soil samples taken using mechanical and hand augers were similar. However, numbers of aphids in samples were influenced by the distance from the trunk at which the samples were taken and the presence and the type of root material in the samples. More aphids were recorded close to the trunk, and at a given distance from the trunk more aphids were recorded if there was root material in the sample, especially if the roots were galled. early autumn (February, March) and declined during winter, especially if the winter rainfall was high. These cycles coincided with the nitrogen cycles in the roots. Embryos were also present in all instars throughout the year. There were more embryos in the 4th instar and adult aphids than in the other instars. The highest number of embryos in the 4th instar and adult aphids occurred during spring, which coincided with peak nitrogen levels in the roots of apple trees. Nitrogen levels in root material adjacent to galls and in ungalled roots were higher than in root galls. A number of entomopathogenic fungi, including species of Conidiobolus, Hirsufella and Beauveria were found. Their present contribution to biological control is not known. A straw mulch suppressed subterranean E. lanigerum population levels at least as well as the soil insecticide, imidacloprid, currently in use. / AFRIKAANSE OPSOMMING: 'n Studie van die basiese biologie van ondergrondse bevolkings van , Eriosoma lanigerum (Hausmann) is in appelboorde in die Weskaap Provinsie van Suid-Afrika uitgevoer. Die afwesigheid van kornikels en die aanwesigheid van 'n vulva kon gebruik word om die 1ste instar nimfe en volwassennes onderskeidelik te identifiseer. Liggaamslengte, liggaamsbreedte en die lengte van die agterste femur kon gebruik word om die 2de , 3de en 4de instars van mekaar te onderskei. Onderskeiding tussen 2de en 3de instar nimfe was egter baie onbetroubaar. Maksimum bevolkingsgroei het by 23°C plaasgevind, terwyl dit nul was by 30 °C. Die beraamde minimum en maksimum temperature vir ontwikkeling was by 4.32 en meer as 30°C onderskeidelik. Getalle van ondergrondse E. lanigerum in grondmonsters wat geneem is met gebruik van meganiese en hand bore was eenders. Getalle plantluise in monsters is egter beïnvloed deur die afstand vanaf die stam waarby die monsters geneem is en die teenwoordigheid van wortelmateriaal in die monsters. Meer plantluise is aangeteken as daar wortelmateriaal in die monsters was, en veral as daar galle op die wortels was. Die appelbloedluis was dwarsdeur die jaar ondergronds aktief. Bevolkingsvlakke het gedurende die vroeë somer (November, Desember) en vroeë herfs (Februarie, Maart) toegeneem, en gedurende die winter afgeneem, veral as die winterreënval hoogwas. Embrio's was ook teenwoordig dwarsdeur die jaar. Daar was meer embrio's in die 4de instar en volwasse plantluise as in die ander instars. Die hoogste aantal embrio's in die 4de instar en volwasse plantluise het in die lente voorgekom, wat saamgeval het met piek stikstofvlakke in die wortels van appelbome. Stikstofvlakke in wortelmateriaal aangrensend aan wortels en in wortels sonder galle was hoër as in wortelgalle. Talle entomopatogeniese swamme, insluitend spesies van Conidiobolus, Hirsufella en Beauvaria IS gevind. Hulle huidige bydrae tot biologiese beheer is nie bekend nie. 'n Strooideklaag het ondergrondse bevolkingsvlakke van E. lanigerum tot ten minste dieselfde mate as die grondinsektedoder, imidacloprid, wat tans in gebruik is, onderdruk.

Thesis (PhD(Agric) (Horticulture))--University of Stellenbosch, 2005. / Bitter pit fruit in commercial consignments of apples still poses an economic threat to exporters from South Africa. Bitter pit develops pre-harvest, but gets progressively worse during storage and is only traceable once the lesions appear after storage. Accurate, early indications of bitter pit incidence will allow for remedial pre-harvest measures in the field, e.g. Ca foliar applications, to reduce the potential losses. Similarly, the automatic detection of a bitter pit fruit during packing will reduce financial losses by identifying unacceptable fruit before shipping. Fluorescence imaging is a fast, non-destructive technique, able to evaluate numerous fruits individually. Results of pre-harvest imaging on apples to identify fruit susceptible to bitter pit showed that pitted fruit were correctly classified, but misclassification of non-pitted fruit with fluorescence imaging was still too high. NIR-spectroscopy point meter readings could distinguish visible bitter pit lesions from healthy tissue. Important wavelengths associated with visible bitter pit were identified. This technique could also identify immature apples, more prone to bitter pit development. It could however not distinguish between bitter pit and non-pitted fruit when applied randomly on the calyx end of apples at harvest. Pre-harvest foliar applications to increase fruit Ca content and reduce bitter pit incidence, is a standard practice world wide. External Ca uptake by fruit was monitored to determine the efficacy of applications during different stages of fruit development. Two periods of efficient uptake of external Ca were identified, viz., cell division and the last few weeks before harvest. Foliar Ca applications from 40 days after full bloom were more effective in increasing fruit Ca content and reducing bitter pit incidence than at 80 days after full bloom, which was recommended previously. Mineral analysis of fruit has been used with variable success to predict bitter pit prior to harvest. The possibility of increasing the accuracy of existing predictive models by using analysis of individual fruit rather than pooled samples, was investigated. By improving the normality of different mineral distributions and decreasing the overlap between pitted and non-pitted fruit classes, it was attempted to improve the reliability of predictions based on variable threshold values. The Ca distribution showed a variation between pitted and nonpitted classes, but still a significant overlap between classes reduced the accuracy of the predictive capacity of this distribution. Even though our results produced a correct classification of 85% for non-pitted fruit, which can be useful, this was still below the required tolerance, of less that 2%, expected on the market. The effect of pruning and fruit bearing position on two-year-old wood on dry mass and Ca allocation of fruit was determined. ‘Golden Delicious’ fruit set was the lowest at the basal bearing position compared to the other positions evaluated and was contrary to expectations. Fruit in a terminal bearing position was superior to the basal position regarding total dry weight and fruit size. Distal wood possibly inhibited growth and set on the basal position via auxin distribution. Ca allocation differed between seasons and cultivars and could either be influenced by bearing position or presence or absence of re-growth.

Thesis (MSc)--Stellenbosch University, 1992. / One copy microfiche. / ENGLISH ABSTRACT: The effects of synthetic pyrethroids on the spider mite, Tetranychus urticae Koch, and its natural enemies was investigated. The pyrethroid cyfluthrin, sprayed for the control of fruit weevil Phlyctinus callosus, did not cause mite outbreaks and was not harmful to the predators when sprayed before they appeared on the apple trees. This spray also gave good control of thrips, bollworm (Heliothis armigera) and fruit weevil (P. callosus). A late season spray of deltamethrin against codling moth, caused an increase in the phytophagous mite population. This was assosiated with a temporary reduction in the population level of the predatory beetle, Oligota fageli. The plants found on the orchard floor were examined. The plant diversity was low and plants that acted as hosts of phytophagous mites during the winter were scarce. However, Solanum nigum carried high mite populations and infected the adjacent apple trees. The plants were too few to have an effect on the whole orchard. Eight synthetic pyrethroids were tested for repellency in a leafdisk dip and spray bioassay using T. urticae. Deltamethrin and fenvalerate caused no walk-off. Cyfluthrin and fluvalinate caused moderate walk-off and bifenthrin, cyhalothrin and lambda-cyhalothrin caused high walk-off. / AFRIKAANSE OPSOMMING: Die invloed van sintetiese piretroIedes op die rooispinmyt, Tetranychus urticae Koch en hul natuurlike vyande is ondersoek. Die piretroIed, cyfluthrin, gespuit vir die beheer van snuitkewer, P4ctinus callosus, het the mytuitbrake veroorsaak the en was ook the skadelik vir predatore nadat dit vroeg in die seisoen, voordat myte in die appelbome verskyn het, gespuit is the. Die bespuiting het ook goeie beheer van blaaspootjies, bolwurm (Heliothis amdgera) en P. callosus gegee. Deltametrien wat later in die seisoen toegedien is vir die beheer van kodlingmot, Cydia pomonella, het 'n mytuitbraak veroorsaak. Dit word geassossieer met die tydelike onderdrukking van die populasievlak van die predatoriese kewer, Oligota fageli. Die plante in die dekgewas is ondersoek. Die plant-verskeidenheid was laag en plante wat kon dien as oorwinterings gashere vir fitofage myte kon dien was skaars. Solanum nigrum het egter groot bevolkings myte gedra wat die appelbome naaste aan hulle eerste besmet het. Daar was egter te min van hierdie plante om 'n invloed op die hele boord te he. Agt piretroIedes is vir afwering van T. urticae in 'n blaarskyf doop en spuit bioessal getoets. Deltamethrin en fenvalerate het geen afwering getoon the. Cyfluthrin en fluvalinate het 'n redelike afwering, terwyl bifenthrin, cyhalothrin en lamda-cyhalothrin het 'n hod mate van afwering getoon

The within-field spatial distribution of F₁, F₂, and F₃ pink bollworm (PBW) (Pectinophora gossypiella Saunders) generations were modeled with Taylor's power law (TPL), Iwao's patchiness regression (IPR), and the geostatistical semivariogram. Kriging interpolation was used to grid data for the generation of isarithmic maps. Distributional patterns and movements within a field are displayed in a time series of three maps depicting density across the field. The sampling protocol was replicated in eight commercial cotton fields in south-central Arizona during 1985 and 1986. Permanent sample stations were situated throughout the fields on a regular grid pattern. Samples were collected during the peak larval population and handled so as to maintain the integrity of site-specific samples (spatially identified by X,Y coordinates). TPL and IPR could not be used satisfactorily to model the F₁ generation. TPL fit the observed F₂ and F₃ data better than IPR. Both methods predicted the F₂ to be more highly aggregated than the F₃. For a given precision, optimum sample size increased when TPL and IPR model parameters were incorporated into sample size formulae relative to a formula which assumed random distribution. Ninety-five percent of the modeled PBW distributions were autocorrelated in 2-dimensional space and shown to conform to regionalized variable theory by the successful application of geostatistics. The semivariogram models are in conceptual agreement with traditional models and represent a worthy alternative to traditional modeling methodology. The semivariogram models have a large nugget effect proportion (average = 67%) which, in combination with low PBW density in commercial fields, limits the applicability of geostatistics in this system. Isarithmic maps showed that F₁ larvae are either localized near a field edge or generally scattered throughout the field. No consistent inter-generational dispersal pattern was identified. The use of systematic grid sampling is most advantageous (relative to random sampling) when density and the spatial dependence of samples is high, or many samples can be taken. Systematic sampling and kriging estimation yielded more precise estimates than random sampling and classical statistics, but the advantage was buffered by low PBW densities and large nugget effect.

The ability of Nabis alternatus Parshley to reduce tobacco budworm, Heliothis virescens (F.), populations was studied in the laboratory, greenhouse and field. Tests were conducted at different temperatures and with different larval instars of tobacco budworm to determine their effects on predatory efficiency. Both immature and adult N. alternatus consumed more first-instars than of either second- or third-instars, or of the egg stage. Temperature significantly affected the predatory capability of N. alternatus. All instars and the adult exhibited a higher rate of consumption at 30°C than at temperatures of 20, 25 and 35°C; adults consumed more tobacco budworm larvae and eggs at all temperatures than did any of the nymphal instars. There were no differences in survival of the different N. alternatus stages at the different temperatures but the average number of days required to complete each instar was affected. Each increase in the predator-to-prey ratio resulted in a reduced survival of the tobacco budworm population. Release rates of 2500, 3750 and 5000 adults per acre resulted in mortalities of 55, 77, and 87%, respectively. Both adult and third-instar N. alternatus exhibited the higher searching and consumptive capacities at different ratios of first-, second-, and third-instar tobacco budworm infestations. All N. alternatus fed more at the 1:4 (predator/prey) ratio than at ratios of 1:1, 1:2, or 1:3. Longevity of adult N. alternatus varied when provided with food substances of sugar solution, green bean, no food or cotton plants at the different temperatures. Survival was greatest when provided with sugar solution over any of the other substrates, and when held at cooler temperatures. Compatibility of N. alternatus with other controls was studied under both laboratory and field conditions. Average longevity in combination with treatments of Elcarᴿ, Bacillus thuringiensis, or fenvalerate was 6.7, 5.9, and 1.3 days, respectively. Compatibility with the biological insecticides was very good and the combinations reduced first-instar tobacco budworm infestations more than did either alone.

Eight "sterol-inhibiting" fungicides were evaluated for in vitro activity against Phymatotrichum omnivorum, and all proved to be very active (EC-50 values ranged from 0.001-0.038 ug/ml). Propiconazol received the major emphasis of this research, which included evaluations of phytotoxicity, soil persistance, resistance development, systemic translocation in cotton, and field evaluations for control of Phymatotrichum Root Rot of cotton. Although propiconazol significantly inhibited mycelial growth of P. omnivorum (in vitro) at concentrations as low as 0.0001 ug/ml within 96 hr, hyphal growth from sclerotia was not affected at 0.1 ug/ml within the same time frame. However, after 168 hr, or if sclerotia were pre-germinated for 120 hr before exposure, growth inhibition was comparable to that of the mycelial cultures. It was speculated that the greater level of sterols in sclerotia masked the inhibition of sterol synthesis by propiconazol until these sterol reserves were depleted. After 5 exposures to propiconazol over a 5 mo period, mycelial growth inhibition was the same as that of mycelium with no previous exposure. This indicated that resistance development should not be an immediate concern. Greenhouse evaluations of phytotoxicity and soil persistance of propiconazol determined that this fungicide can severely stunt cotton if planted into treated soil. Using stunting of seedlings as a bioassy of the persistance of propiconazol in non-sterilized soil, it was found that propiconazol was still active 3-5 mo after the initial soil treatment. Through the application of C-14 labeled propiconazol to the leaves of 5 and 8-wk old cotton plants, it was determined that no more than 0.23% of the applied radioactivity was translocated to the roots. However, based upon these percentages, root weights of the plants, and the amount of propiconazol applied to each plant during a field application, the theoretical concentration in the roots would be 30-700X the in vitro concentration necessary to inhibit mycelial growth of P. omnivorum (EC-50 = 0.003-0.006 ug/ml). Field evaluations of propiconazol were conducted in 1982 and 1983, while etaconazol, triadimefon, triadimenol, imazalil, and XE-779 were evaluated in 1983. These evaluations determined that propiconazol, etaconazol, and triadimenol showed promise for control of this disease, while imazalil, triadimefon, and XE-779 did not. . . . (Author's abstract exceeds stipulated maxium length. Discontinued here with permission of author.) UMI

Survey of crops of common bean (Phaseolus vulgaris L.) in Sonora, Mexico revealed the presence of two isometric viruses and one flexuous rod virus on the basis of host reaction, particle morphology, serology and physico-chemical properties. The isometric viruses were identified as Bean Southern Mosaic Virus (BSMV) and Cowpea Chlorotic Mottle Virus (CCMV); the flexuous rod virus was identified as Bean Common Mosaic Virus (BCMV). Using bean cultivar differentials, two strains of the potyvirus BCMV were identified, NY-15 and a previously undescribed strain designated YV-1. Host range, serological tests, and RNA electrophoresis indicated that the Sonoran BSMV cultures are similar to BSMV-strain A. Serology and RNA-electrophoresis indicated that the Sonoran CCMV isolates are identical to CCMV-strain A. BSMV and CCMV were always isolated as a mixture from seed lots and from field collected bean tissue. BCMV occurred alone or in mixed infections with BSMV and CCMV. BCMV was seed transmitted with an average efficiency of 58 percent. The BSMV-CCMV mixture was transmitted with an efficiency of 6 percent. BSMV and CCMV were seed transmitted together, but separate transmission of BSMV or CCMV was not detected. Commercial seed lots from two major bean growing regions of Sonora (Hermosillo Coast, Sonora River) were contaminated with the BSMV-CCMV mixture but not with BCMV. The average contamination level was 13 percent. Two common weeds present in Sonoran agricultural areas were found to be potential alternate hosts of CCMV. Both Sisymbrium irio L. and Melilotus indica L. were infected systemically, although the infection in M. indica was latent. Potential losses due to Sonoran bean viruses were measured in greenhouse experiments with the cultivar Pinto 111. BCMV strains caused a 29.4 to 60.1% reduction, whereas BSMV-CCMV mixtures induced a 22.5 to 74.6% yield reduction. A synergism occurred between the BSMV-CCMV mixture and BCMV resulting in more severe symptoms and a yield reduction of 92.7%. Synergistic effects were also observed between BSMV and CCMV. Actual yield reduction resulted from impaired flower production and, consequently, reduced pod production. Significant effects on plant tissue production, flower fertilization and seed quality were not observed. Cowpea chlorotic mottle virus infected mung bean (Vigna radiata (L.) Wilczek) a previously unreported host. Infection of mung bean by BSMV was only possible when CCMV was present in the inoculum. Both BSMV and CCMV could be isolated from symptomatic plants infected with the BSMV-CCMV mixture, however, symptoms on mung bean were unchanged from infection by CCMV alone.