Genetic characterisation of a range of geographically distinct Helicoverpa armigera nucleopolyhedrovirus (HearNPV) isolates and evaluation of biological activity against South African populations of the African bollworm, Helicoverpa armigera (Hu bner) (Lepidoptera: Noctuidae)
- Mtambanengwe, Kudzai Tapiwanashe Esau
- Authors: Mtambanengwe, Kudzai Tapiwanashe Esau
- Date: 2019
- Subjects: Helicoverpa armigera -- Biological control -- South Africa , Baculoviruses -- Genetics , Agricultural pests -- Biological control -- South Africa
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/97334 , vital:31426
- Description: The African bollworm, Helicoverpa armigera Hübner (Lepidoptera: Noctuidae) is a pest of economic and agricultural importance globally. It is a polyphagous pest that feeds on a wide range of host plants including economically important crops. The impact it has on agricultural systems makes its control a priority. The most common method of control is using chemical pesticides; however, continuous application of the pesticides has resulted in the development of resistance. The use of biological control has been investigated and established as an effective method of control as a standalone or part of an integrated pest management (IPM) system. The use of the baculovirus Helicoverpa armigera nucleopolyhedrovirus (HearNPV), has shown promise in the control of H. armigera. Commercial formulations based on the virus are available in many global markets. However, the identification of novel HearNPV isolates will aid in the control of H. armigera as well as provide alternative isolates that may have better virulence. Three new HearNPV isolates were purified and identified from three distinct geographical South African locations H. armigera cadavers and named HearNPV-Albany, HearNPV-KZN and HearNPV-Haygrove. The genomes of two of the HearNPV isolates, namely HearNPV-Albany and HearNPV-KZN were genetically characterised and compared to other geographically distinct HearNPV isolates. Virulence studies were performed comparing the new HearNPV isolates against established commercial HearNPV formulations, Helicovir™ and Helicovex® and other geographically distinct isolated HearNPV, HearNPV-G4 and HearNPV-SP1. Two laboratory colonies were established using H. armigera collected from South African fields in the Belmont Valley near Grahamstown labelled as Albany colony and a colony provided from Haygrove Eden farm near George labelled as Haygrove colony. Biological studies were carried out using the Albany H. armigera colony comparing the rate of development, survival and fertility on bell green peppers, cabbage leaves and on artificial diet. From the biological studies, it was recorded that development and survivorship was best on artificial diet. Regular quality control was required for the maintenance of the colony and continuous generations of healthy larvae were eventually established. Diseased cadavers with signs of baculovirus infection were collected after bioprospecting from the Kwa-Zulu Natal Province in South Africa and were labelled KZN isolate; Belmont Valley near Grahamstown and were labelled Albany isolate; and Haygrove Eden farm near George and were labelled Haygrove isolate for the study. A fourth isolate made up of a crude extract of occlusion bodies (OBs) first described by Whitlock was also analysed and labelled Whitlock isolate. Occlusion bodies were extracted, purified and morphologically identified from the KZN, Albany, Haygrove and Whitlock isolates using TEM. Genomic DNA, which was extracted from the purified OBs. Using PCR, the identity of the OBs as HearNPV was confirmed. Genomic analyses were performed on HearNPV-Albany and HearNPV-KZN through genetic characterisation and comparison with other geographically distinct HearNPV genomes to confirm novelty and establish potential genetic relationships between the isolates through evolutionary distances. Full genomic sequencing of the isolated HearNPV and comparison with other geographically distinct HearNPV isolates identified genomic differences that showed that the HearNPV isolates were novel. HearNPV-Albany and HearNPV-KZN were successfully sequenced and identified as novel isolates with unique fragment patterns and unique gene sequences through deletions or insertions when compared to other geographically distinct HearNPV. This raised the potential for differences in biological activity against H. armigera larvae when tested through biological assays. HearNPV-Whit genome assembly had low quality data which resulted in many gaps and failed assembly. The biological activity of HearNPV isolates from Spain, China, South Africa and two commercial formulations were studied against the laboratory established H. armigera South African colony. The LC50 values of the different South African HearNPV isolates were established to be between 7.7 × 101 OBs.ml-1 for the most effective and 3.2 × 102 OBs.ml-1 for the least effective. The Spanish and Chinese HearNPV isolates resulted in LC50 values of 2.0 × 102 OBs.ml-1 and 1.2 × 101 OBs.ml-1 respectively. The commercial formulations resulted in the least virulence observed with an LC50 of 5.84× 102 OBs.ml-1 and 9.0 × 102 OBs.ml-1 for Helicovex® and Helicovir™ respectively. In this study, novel South African HearNPV isolates were isolated and identified. Through characterisation and bioassays against South African H. armigera populations the HearNPV isolates were shown to have different virulence in comparison to geographically distinct isolates. From this research, there is potential for development of new H. armigera biopesticides based on the novel isolates after field trial testing.
- Full Text:
- Date Issued: 2019
- Authors: Mtambanengwe, Kudzai Tapiwanashe Esau
- Date: 2019
- Subjects: Helicoverpa armigera -- Biological control -- South Africa , Baculoviruses -- Genetics , Agricultural pests -- Biological control -- South Africa
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/97334 , vital:31426
- Description: The African bollworm, Helicoverpa armigera Hübner (Lepidoptera: Noctuidae) is a pest of economic and agricultural importance globally. It is a polyphagous pest that feeds on a wide range of host plants including economically important crops. The impact it has on agricultural systems makes its control a priority. The most common method of control is using chemical pesticides; however, continuous application of the pesticides has resulted in the development of resistance. The use of biological control has been investigated and established as an effective method of control as a standalone or part of an integrated pest management (IPM) system. The use of the baculovirus Helicoverpa armigera nucleopolyhedrovirus (HearNPV), has shown promise in the control of H. armigera. Commercial formulations based on the virus are available in many global markets. However, the identification of novel HearNPV isolates will aid in the control of H. armigera as well as provide alternative isolates that may have better virulence. Three new HearNPV isolates were purified and identified from three distinct geographical South African locations H. armigera cadavers and named HearNPV-Albany, HearNPV-KZN and HearNPV-Haygrove. The genomes of two of the HearNPV isolates, namely HearNPV-Albany and HearNPV-KZN were genetically characterised and compared to other geographically distinct HearNPV isolates. Virulence studies were performed comparing the new HearNPV isolates against established commercial HearNPV formulations, Helicovir™ and Helicovex® and other geographically distinct isolated HearNPV, HearNPV-G4 and HearNPV-SP1. Two laboratory colonies were established using H. armigera collected from South African fields in the Belmont Valley near Grahamstown labelled as Albany colony and a colony provided from Haygrove Eden farm near George labelled as Haygrove colony. Biological studies were carried out using the Albany H. armigera colony comparing the rate of development, survival and fertility on bell green peppers, cabbage leaves and on artificial diet. From the biological studies, it was recorded that development and survivorship was best on artificial diet. Regular quality control was required for the maintenance of the colony and continuous generations of healthy larvae were eventually established. Diseased cadavers with signs of baculovirus infection were collected after bioprospecting from the Kwa-Zulu Natal Province in South Africa and were labelled KZN isolate; Belmont Valley near Grahamstown and were labelled Albany isolate; and Haygrove Eden farm near George and were labelled Haygrove isolate for the study. A fourth isolate made up of a crude extract of occlusion bodies (OBs) first described by Whitlock was also analysed and labelled Whitlock isolate. Occlusion bodies were extracted, purified and morphologically identified from the KZN, Albany, Haygrove and Whitlock isolates using TEM. Genomic DNA, which was extracted from the purified OBs. Using PCR, the identity of the OBs as HearNPV was confirmed. Genomic analyses were performed on HearNPV-Albany and HearNPV-KZN through genetic characterisation and comparison with other geographically distinct HearNPV genomes to confirm novelty and establish potential genetic relationships between the isolates through evolutionary distances. Full genomic sequencing of the isolated HearNPV and comparison with other geographically distinct HearNPV isolates identified genomic differences that showed that the HearNPV isolates were novel. HearNPV-Albany and HearNPV-KZN were successfully sequenced and identified as novel isolates with unique fragment patterns and unique gene sequences through deletions or insertions when compared to other geographically distinct HearNPV. This raised the potential for differences in biological activity against H. armigera larvae when tested through biological assays. HearNPV-Whit genome assembly had low quality data which resulted in many gaps and failed assembly. The biological activity of HearNPV isolates from Spain, China, South Africa and two commercial formulations were studied against the laboratory established H. armigera South African colony. The LC50 values of the different South African HearNPV isolates were established to be between 7.7 × 101 OBs.ml-1 for the most effective and 3.2 × 102 OBs.ml-1 for the least effective. The Spanish and Chinese HearNPV isolates resulted in LC50 values of 2.0 × 102 OBs.ml-1 and 1.2 × 101 OBs.ml-1 respectively. The commercial formulations resulted in the least virulence observed with an LC50 of 5.84× 102 OBs.ml-1 and 9.0 × 102 OBs.ml-1 for Helicovex® and Helicovir™ respectively. In this study, novel South African HearNPV isolates were isolated and identified. Through characterisation and bioassays against South African H. armigera populations the HearNPV isolates were shown to have different virulence in comparison to geographically distinct isolates. From this research, there is potential for development of new H. armigera biopesticides based on the novel isolates after field trial testing.
- Full Text:
- Date Issued: 2019
Use of microbial fuel cells in the beneficiation of algal biomass for bioelectricity production
- Mtambanengwe, Kudzai Tapiwanashe Esau
- Authors: Mtambanengwe, Kudzai Tapiwanashe Esau
- Date: 2015-04-10
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/480334 , vital:78432
- Description: Microbial fuel cells (MFCs) offer an alternative technology that is able to convert organic matter into electrical energy by making use of bacterial biomass as the biocatalysts. Performance of the MFCs is dependent on many factors such as substrate, biocatalyst, electrode material and optimum operational conditions including temperature and pH. Significant research has been conducted on the use of different substrates to fuel the MFC. The possibility of harvesting energy from organic waste sources in the MFC makes the technology attractive. In this study, we have investigated the use of Chlorella, Arthrospira and a mixed algal consortium obtained from the local wastewater treatment facility in Grahamstown, courtesy of the Institute for Environmental Biotechnology, Rhodes University (EBRU) as feedstock in an MFC with Enterobacter cloacae as the biocatalyst. Pre-treatment of the algae-based feedstock was studied as well as the influence of treatment on nutrient release and biocatalyst performance during growth studies and MFC operations. Sonication, autoclaving and a combination of the two were used as the pre-treatment methods. Pre-treatment resulted in the release of nutrients from algal cells to the media. Peak nutrient realease was observed when a combination of sonicating and autoclaving was employed. Sonicating and autoclaving the mixed consortium from EBRU resulted in an MFC peak power density of 101.2 (± 4.58) mW.m-2. This represented more than 80% of the peak power density obtained in RCM medium. Operational conditions during MFC studies such as pH, temperature, nutrient utilisation by the biocatalyst and performance of the proton exchange membrane were measured during the course of the study. Growth kinetics and MFC operations were shown to be optimal when the substrate feedstock was acidic. However, for longer MFC operations (120 hours), total power output was greater by 3 to 5 fold when the feedstock was at acidic pH (4-6) than when the pH of the substrate feedstock was alkaline (8 and 9). Further MFC studies were performed on the effect of electrode materials including activated carbon fibre and carbon paper. The study examined also the use of live Chlorella and Arthrospira cultures as biocathodes in an MFC. We also showed that activated carbon fibre performs well as an electrode catalyst for both anode and cathode without any need of modification. Biocathode studies showed that the main limiting factor to biocathodes performance was light irradiance. , Thesis (MSc) -- Faculty of Science, Biotechnology Innovation Centre, 2015
- Full Text:
- Date Issued: 2015-04-10
- Authors: Mtambanengwe, Kudzai Tapiwanashe Esau
- Date: 2015-04-10
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/480334 , vital:78432
- Description: Microbial fuel cells (MFCs) offer an alternative technology that is able to convert organic matter into electrical energy by making use of bacterial biomass as the biocatalysts. Performance of the MFCs is dependent on many factors such as substrate, biocatalyst, electrode material and optimum operational conditions including temperature and pH. Significant research has been conducted on the use of different substrates to fuel the MFC. The possibility of harvesting energy from organic waste sources in the MFC makes the technology attractive. In this study, we have investigated the use of Chlorella, Arthrospira and a mixed algal consortium obtained from the local wastewater treatment facility in Grahamstown, courtesy of the Institute for Environmental Biotechnology, Rhodes University (EBRU) as feedstock in an MFC with Enterobacter cloacae as the biocatalyst. Pre-treatment of the algae-based feedstock was studied as well as the influence of treatment on nutrient release and biocatalyst performance during growth studies and MFC operations. Sonication, autoclaving and a combination of the two were used as the pre-treatment methods. Pre-treatment resulted in the release of nutrients from algal cells to the media. Peak nutrient realease was observed when a combination of sonicating and autoclaving was employed. Sonicating and autoclaving the mixed consortium from EBRU resulted in an MFC peak power density of 101.2 (± 4.58) mW.m-2. This represented more than 80% of the peak power density obtained in RCM medium. Operational conditions during MFC studies such as pH, temperature, nutrient utilisation by the biocatalyst and performance of the proton exchange membrane were measured during the course of the study. Growth kinetics and MFC operations were shown to be optimal when the substrate feedstock was acidic. However, for longer MFC operations (120 hours), total power output was greater by 3 to 5 fold when the feedstock was at acidic pH (4-6) than when the pH of the substrate feedstock was alkaline (8 and 9). Further MFC studies were performed on the effect of electrode materials including activated carbon fibre and carbon paper. The study examined also the use of live Chlorella and Arthrospira cultures as biocathodes in an MFC. We also showed that activated carbon fibre performs well as an electrode catalyst for both anode and cathode without any need of modification. Biocathode studies showed that the main limiting factor to biocathodes performance was light irradiance. , Thesis (MSc) -- Faculty of Science, Biotechnology Innovation Centre, 2015
- Full Text:
- Date Issued: 2015-04-10
- «
- ‹
- 1
- ›
- »