53 research outputs found

    BIOCONTROL OF PHYTOPHTHORA CINNAMOMI ON AVOCADO: IDENTIFICATION AND FIELD TESTING OF LOCAL NATURAL ANTAGONISTS, AND EVALUATION OF ROOTSTOCKS FOR RESISTANCE

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    Abstract Soils suppressive to root rot of avocado (caused by Phytophthora cinnamomi), were first identified in South Africa in 1990. Mcro-organisms from these soils were tested for in vitro antagonism to Phytophthora cinnamomi and subsequently evaluated for suppression of root rot of avocado seedling plants in a mistbed. Three fungal antagonists, Paecilomyces filacinus, Aspergillus candidus and Trichoderma hamatum were effective in suppressing root rot. These antagonists have been evaluated since 1992 for control of root rot in avocado trees in the field. Populations of the antagonists have been found to increase in the root zone of newly planted trees (after antagonist treatment in the nursery and in the orchard) and in the root zone of established Hass and Fuerte trees planted in 1981 and 1980 (after antagonist treatment in the orchard). In an isolated planting site consisting of various ungrafted avocado rootstocks (eg. G1033, Dusa, Latas, D9, Duke 7, Barr Duke, Thomas, Velvic) trees undergo open pollination. Seeds from this orchard, situated at Westfalia Estate, are germinated and the seedlings evaluated for resistance to root rot in a mistbed. A number of successful selections have been made and these are being clonally propagated and grafted with Hass. These trees are to be planted in a root rot infested field site where they will be evaluated for yield and resistance to root rot

    Using biomarkers to predict TB treatment duration (Predict TB): a prospective, randomized, noninferiority, treatment shortening clinical trial

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    Background : By the early 1980s, tuberculosis treatment was shortened from 24 to 6 months, maintaining relapse rates of 1-2%. Subsequent trials attempting shorter durations have failed, with 4-month arms consistently having relapse rates of 15-20%. One trial shortened treatment only among those without baseline cavity on chest x-ray and whose month 2 sputum culture converted to negative. The 4-month arm relapse rate decreased to 7% but was still significantly worse than the 6-month arm (1.6%, P<0.01).  We hypothesize that PET/CT characteristics at baseline, PET/CT changes at one month, and markers of residual bacterial load will identify patients with tuberculosis who can be cured with 4 months (16 weeks) of standard treatment.Methods: This is a prospective, multicenter, randomized, phase 2b, noninferiority clinical trial of pulmonary tuberculosis participants. Those eligible start standard of care treatment. PET/CT scans are done at weeks 0, 4, and 16 or 24. Participants who do not meet early treatment completion criteria (baseline radiologic severity, radiologic response at one month, and GeneXpert-detectable bacilli at four months) are placed in Arm A (24 weeks of standard therapy). Those who meet the early treatment completion criteria are randomized at week 16 to continue treatment to week 24 (Arm B) or complete treatment at week 16 (Arm C). The primary endpoint compares the treatment success rate at 18 months between Arms B and C.Discussion: Multiple biomarkers have been assessed to predict TB treatment outcomes. This study uses PET/CT scans and GeneXpert (Xpert) cycle threshold to risk stratify participants. PET/CT scans are not applicable to global public health but could be used in clinical trials to stratify participants and possibly become a surrogate endpoint. If the Predict TB trial is successful, other immunological biomarkers or transcriptional signatures that correlate with treatment outcome may be identified. TRIAL REGISTRATION: NCT02821832

    An assessment of the potential of irradiation as a postharvest control treatment against the banded fruit weevil, Phlyctinus callosus (Coleoptera: Curculionidae): effects on adult weevils and host fruit (‘Flavor Fall’ pluots)

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    Thesis (MScAgric)--Stellenbosch University, 2013.ENGLISH ABSTRACT: The export of South African fruit to some of its biggest international markets may be rejected if the phytosanitary pest, Phlyctinus callosus (Coleoptera: Curculionidae) is found in fruit consignments. An alternative to methyl bromide fumigation is needed and one of the most promising of the alternative treatments is phytosanitary irradiation as it is environmentally friendly, does not leave residues on food or in the environment and it is effective against a wide variety of insects. Field-collected weevils were treated with five doses of gamma irradiation (5, 10, 20, 40 and 80 Gy) and the fecundity and fertility of mating crosses of treated males and females with treated and untreated individuals of the opposite sex, were determined to evaluate the effect on P. callosus reproductive ability post-treatment. Results indicated that irradiation treatment did not affect fecundity, but fertility was significantly affected, decreasing as the irradiation dose increased. Females were more susceptible to the irradiation treatment than males, and after treatment with 80 Gy, eggs laid by females and mated with either treated or untreated males, did not hatch. A generic dose of 400 Gy for all insect pests except tephritid fruit flies and pupae and adult Lepidoptera is currently approved by USDA-APHIS (United States Department of Agriculture – Animal and Plant Health Inspection Services) for use on certain commodities. Results from the present study support the development of a species-specific dose for P. callosus, as well as the development of a group generic dose for the Curculionidae that is lower than 400 Gy. Effective phytosanitary irradiation treatments are only feasible if the treatment does not adversely affect fruit quality and the marketability of export fruit. Therefore, an investigation of the effects of irradiation disinfestations treatments on the quality of the new pluot cultivar, ‘Flavor Fall’ was made. Packed cartons were treated with three doses of gamma irradiation: 400 Gy, 900 Gy and 1400 Gy. After treatment fruit underwent a PD 7 dual temperature cold storage regime for 42 days and a shelf-life simulation for 7 days. The impact of insect-proof bags, sometimes required by importing countries to keep insects off packaged fruit, was also investigated. Respiration rate of the fruit was measured throughout and fruit quality evaluations were done after cold storage and after shelf-life. The results indicated that quality parameters measured at the end of cold storage, which would be after the fruit arrives at the export markets, were above the minimum standards for overseas markets. Gel breakdown was unacceptably high after the higher temperature exposure of shelf-life for fruit treated with the 900 and 1400 Gy doses. The insect-proof bags reduced shrivel, but resulted in higher incidence of gel breakdown. The use of irradiation, together with the use of the insect-proof bag, has potential as an alternative postharvest mitigation treatment for plums. Lastly, an investigation into potential rearing methods for P. callosus, including recommendation for the future, was made as the availability of a sustainable rearing method that ensures a consistent supply of high quality P. callosus adults would enable continuous research with greater numbers of this pest. The information generated in this study provides a greater understanding of the radiation biology of, not only this curculionid species, but the Curculionidae as a group, and is valuable in advancing the development of alternative postharvest control measures against this phytosanitary pest.AFRIKAANSE OPSOMMING: Suid Afrikaanse vrugte uitvoere na van die grootste internasionale markte mag weg gewys word as die fitosanitêre pes, Phlyctinus callosus (Coleoptera: Curculionidae) in die versending gevind word. ‘n Alternatief vir metiel bromied beroking word benodig en een van die mees belowende alternatiewe behandelings is fitosanitêre bestraling aangesien dit omgewings vriendelik is, nie residue op kos of in die omgewing los nie, en effektief is teen ‘n wye verskeidenheid van insekte. Veldversamelde kalanders is behandel met vyf dosisse gamma bestraling (5, 10, 20, 40 en 80 Gy) waarna die vrugbaarheid van paringskruisings bepaal is deur kruisings tussen behandelde manlike en vroulike kalanders met behandelde en nie-behandelde individue van die teenoorgestelde geslag te maak, en so die na-behandelings effek op die voortplantings vermoeë van P. callosus te evalueer. Die resultate het getoon dat die bestralings behandeling geen invloed gehad het op die hoeveelheid eiers wat gelê is nie, maar dat die uitbroei van eiers aanduidend geaffekteer is deur die behandeling. Die hoeveelheid eiers wat uitgebroei het, het minder geraak soos die bestralings behandeling toegeneem het. Vroulike kalanders was meer sensitief vir die behandeling en na 80 Gy, of hul gekruis is met behandelde of niebehandelde mannetjies, het geen eiers uitgebroei nie. ‘n Generiese dosis van 400 Gy vir alle insekte, uitsluitend tephritiese vrugte vlieë en papies en volwasse Lepidoptera is huidiglik goedgekeur deur die USDA-APHIS (United States Department of Agriculture – Animal and Plant Health Inspection Services) vir sekere kommoditeite. Die resultate van die huidige studie ondersteun die ontwikkeling van ‘n spesie-spesifieke dosis vir P. callosus, so ook die ontwikkeling van ‘n generiese groep dosis vir Curculionidae wat laer as 400 Gy is. Effektiewe fitosanitêre bestralings behandeling is slegs moontlik indien die behandelings dosis nie nadelig vir vrugkwaliteit en die bemarking van uitvoer vrugte is nie. Dus is die effek wat bestralings bestryding behandeling op die kwaliteit van ‘n nuwe pluot kultivar, ‘Flavor Fall’ ondersoek. Vrugte verpak in kartonne is met drie dosisse gamma bestraling behandel: 400 Gy, 900 Gy en 1400 Gy. Na behandeling is die vrugte deur ‘n PD 7 dubbel temperatuur koelopbergings regime van 42 dae en rak-lewe simulasie vir 7 dae gesit. Die impak van insek-bestande sakke wat insekte van die verpakte vrugte weg hou en soms deur invoerende lande ‘n vereiste is, is ook ondersoek. Respirasie tempo van die vrugte is getoets en vrugkwaliteit evaluasies is gedoen na koelopberging en rak-lewe. Die resultate het getoon dat die kwaliteits maatstawwe wat getoets is na koelopberging (wat tipies is wanneer die vrugte by die uitvoer mark arriveer), almal bo die minimum standaarde van die uitvoer markte was. Gel-afbraak was onaanvaarbaar hoog na blootstelling aan die hoër temperature tydens rak-lewe vir vrugte wat behandel is met 900 en 1400 Gy. Die insek-bestande sakke het verrimpeling verminder, maar die voorkoms van gel-afbraak vermeerder. Die gebruik van bestraling, tesame met die insek-bestande sakke, het potensiaal as alternatiewe na-oes behandeling vir pruime. Laastens is ‘n ondersoek ingestel vir moontlike teeltegnieke vir P. callosus en aanbevelings gemaak vir toekomstike studies. Die beskikbaarheid van ‘n volhoubare teeltegniek wat konstante, hoë kwaliteit P. colossus individue verskaf sal aaneenlopende navorsing met groter getalle van die pes moontlik maak. Die inligting wat deur hierdie studie gegenereer is help om die bestralings biologie, nie net van hierdie curculionid spesie nie, maar die Curculionidae as ‘n groep te verstaan, en is kosbaar in die bevordering van ontwikkeling van alternatiewe na-oes beheer meganismes teen hierdie fitosanitêre pes

    The Photosynthetic Efficiency and Carbohydrates Responses of Six Edamame (<i>Glycine max</i>. L. Merrill) Cultivars under Drought Stress

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    Vegetable-type soybean, also known as edamame, was recently introduced to South Africa. However, there is lack of information on its responses to drought. The aim of this study was to investigate the photosynthetic efficiency and carbohydrates responses of six edamame cultivars under drought stress. Photosynthetic efficiency parameters, including chlorophyll fluorescence and stomatal conductance, were determined using non-invasive methods, while pigments were quantified spectrophotometrically. Non-structural carbohydrates were quantified using Megazyme kits. Structural carbohydrates were determined using Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). Drought stress significantly increased the Fv/Fm and PIabs of AGS429 and UVE17 at pod filling stage. Chlorophyll-a, which was most sensitive to drought, was significantly reduced in AGS429 and UVE17, but chlorophyll-b was relatively stable in all cultivars, except UVE17, which showed a significant decline at flowering stage. AGS354 and AGS429 also showed reduced chlorophyll-b at pod filling. UVE17 showed a significant reduction in carotenoid content and a substantial reduction in stomatal conductance during pod filling. Drought stress during pod filling resulted in a significant increase in the contents of trehalose, sucrose and starch, but glucose was decreased. Chlorophyll-a positively correlated with starch. The FTIR and XRD results suggest that the cell wall of UVE14, followed by UVE8 and AGS429, was the most intact during drought stress. It was concluded that carotenoids, stomatal conductance, starch and hemicellulose could be used as physiological/biochemical indicators of drought tolerance in edamame. This information expands our knowledge of the drought defense responses in edamame, and it is essential for the physiological and biochemical screening of drought tolerance
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