Browsing by Author "Mbili, Nokwazi Carol."

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Biocontrol agents in combination with moringa oleifera leaf extract for integrated control of botrytis cinerea of tomato.
(2022) Malevu, Nonkanyiso.; Mbili, Nokwazi Carol.; Magwaza, Lembe Samukelo.
Tomatoes and tomato-based foods provide essential nutrients beneficial to human health. Despite these benefits from tomatoes, postharvest losses result in unprofitable tomato production in some parts of the world. During ripening and harvesting, tomato becomes susceptible to diseases resulting in shorter shelf life. Susceptibility of tomato plants to Botrytis cinerea which causes grey mould infection can occur at any growth stage and the most susceptible growth stage is during ripening and senescing. Factors such as mechanical injuries, inadequate storage conditions, inappropriate handling, and transport affect tomato quality. The use of chemicals not only negatively affects farmers' yield by further enhancing pesticide resistance to crop pathogens but also influences other sectors of communities through contamination of drinking water sources which is an environmental hazard. There is a need to emphasise and encourage sustainable agricultural strategies such as biological control and plant extracts as alternative strategies which are eco-friendly and economically sustainable. Therefore, the main aim of this research was to examine the effect of biocontrol agents and Moringa oleifera leaf extract, individually and in combination, to control B. cinerea on tomatoes in vitro and in vivo. A total of 48 biocontrol agents were isolated from different parts of tomato leaves, citrus leaves, mushrooms and erect prickly pear. The isolates were screened against B. cinerea for the inhibitory effect and as potential control of the pathogen on potato dextrose agar (PDA) and tomato fruits. Serratia marcescens, Bacillus pumilus and Bacillus safensis inhibited B. cinerea by more than 50% in vitro. During in vivo screening, Serratia and Bacillus isolates inhibited grey mould incidence on ‘Jam’ tomatoes by more than 70%. The scanning electron microscopy images of the pathogen samples treated with biocontrol agents showed swollen and lysed mycelia. Moringa leaf extracts (MLE) were prepared into four concentrations MLE 1%, MLE 2%, MLE 3% and MLE 4%. The MLE concentrations were tested for their antifungal activity on the pathogen growth during in vitro studies. High concentrations were found to have some inhibitory effect on the mycelial growth of B. cinerea. There was no significant difference observed in the control, MLE 1% and MLE 2% since no mycelial inhibition was observed after 7 days at 25°C. For in vivo studies, all the concentrations had some inhibitory effect against grey mould on ‘Jam’ tomatoes. This was evidenced by lower disease incidence observed on the fruits treated with the moringa leaf extract compared to the control treatment. Scanning electron micrographs showed morphological changes in the hyphae on the samples treated with concentrations of MLE and there was also a breakage on the pathogen hyphae. Furthermore, this study evaluated the integrated control of B. cinerea using S. marcescens, B. safensis and B. pumilus integrated with MLE 2% and MLE 3% in vitro and in vivo. S. marcescens, B. safensis and B. pumilus integrated with MLE 2% and MLE 3% successfully suppressed mycelial growth of B. cinerea in vitro. Treating tomato fruits with S. marcescens, B. safensis and B. pumilus integrated with MLE 2% and MLE 3% reduced the disease incidence of grey mould compared to the control. The SEM images of the mycelial growth of B. cinerea showed shrinkage, and breakage of pathogen mycelia and the spores were damaged showing breakage and immature spores both in vitro and in vivo. Integrating moringa leaf extract, Serratia spp. and Bacillus spp. have the potential to be an alternative to synthetic fungicides to control postharvest pathogens.
Evaluation of integrated control of postharvest grey mould and blue mould of pome fruit using yeast, potassium silicate and hot water treatments.
(2012) Mbili, Nokwazi Carol.; Laing, Mark Delmege.; Yobo, Kwasi Sackey.
The public concern over synthetic pesticides in foods and the environment has created an interest to find effective and safe non-fungicide means of controlling postharvest pathogens. The overall objective of this thesis was to evaluate the effect of potassium silicate, yeast antagonists and hot water dip treatment to control postharvest grey mould and blue mould of pome fruits, caused by Botrytis cinerea and Penicillium expansum, respectively. Botrytis cinerea and Penicillium expansum were isolated from infected strawberry and pear fruits, respectively. These isolates were found to be non-resistant to YieldPlus® (Anchor yeast, Cape Town, South Africa), a biofungicide containing a yeast Cryptococcus albidus. A total of 100 epiphytic yeast isolates were obtained from the fruit surface of “Golden Delicious” apples and “Packham’s Triumph” pears, and screened against B. cinerea and P. expansum. Fifteen yeast isolates reduced grey mould incidence by > 50%, when applied four hours before inoculation with B. cinerea. Similarly, seven yeast isolates reduced blue mould incidence by > 50%, when applied four hours before inoculation with P. expansum. YieldPlus® and yeast Isolate YP25 provided the best control of B. cinerea, while Isolate YP60 and YieldPlus® provided the best control of P. expansum on “Golden Delicious” apples. A mixture of YP25 and YP60 provided complete control of both B. cinerea and P. expansum, when applied to “Golden Delicious” apples before inoculation with either B. cinerea or P. expansum. Electron microscopy studies showed that yeast Isolates YP25 and YP60 inhibited the mycelial growth of B. cinerea and P. expansum, respectively. Preventative and curative application of potassium silicate resulted in reduced incidence of B. cinerea or P. expansum of “Golden Delicious” apples. Electron microscopy studies indicated that potassium silicate inhibited the growth of B. cinerea and P. expansum. Furthermore, treatment of “Golden Delicious” apples with either potassium chloride or potassium hydroxide resulted in reduced incidence of both B. cinerea and P. expansum. In vivo tests showed that the disease incidence of P. expansum and B. cinerea on “Golden Delicious” apples was reduced by hot water dip treatments at 58-60°C for 60 to 120 seconds, compared with the control fruit treated with sterile distilled water, without causing skin damage. The use of potassium silicate, yeasts (Isolates YP25 and YP60), YieldPlus® and the antagonists mixture (YP25+YP60) in combination, resulted in the control of B. cinerea and P. expansum of “Golden Delicious” apples compared with Imazalil® treated fruit.
Integrated control of postharvest Fusarium solani of potatoes using UV-C irradiation and Moringa oleifera leaf extracts.
(2024) Buthelezi, Gcinokuhle.; Mbili, Nokwazi Carol.; Mditshwa, Asanda.
Potatoes are a source of food, income and important nutrients which are beneficial to human health. However, production of potato tuber may be hindered by postharvest losses, which reduce the quality and quantity of potatoes reaching consumers. Major losses of potatoes are caused by poor harvesting, sorting, cleaning, handling, and packing. Fusarium solani, a causal agent of dry rot disease that mainly affects potatoes occurs during storage as the pathogen invades the potato tuber through tissue injuries inflicted during lifting or grading. Fusarium dry rot has been mainly controlled by using chemicals. However, the frequent use of chemicals has been recently reported to enhance fungicide resistance to potato pathogens. Chemical fungicides also negatively affect human health and the environment, as they introduce residues in treated potatoes and soil. There is a need to investigate and develop sustainable agricultural strategies such as UV-C irradiation and plant extracts as alternative strategies which are human and environmentally friendly. Therefore, this research aimed to evaluate the effect of UVC irradiation and Moringa oleifera leaf extract, independently and their combined effect in controlling F. solani on potatoes in vitro and in vivo. The antifungal effects of UV-C irradiation against F. solani were evaluated in vitro and in vivo. UV-C treatment for 10 and 15 minutes at a 10 cm distance successfully inhibited the mycelial growth of F. solani by ≥ 50% at 7-day post-inoculation. The in vivo results showed that ‘Sifra’ potatoes treated with UV-C for 10 minutes and 15 minutes had a disease incidence ≤ 33%. The increase in the duration of UV-C exposure to potatoes lowered the disease incidence on potatoes. The scanning electron icrographs showed the breakage and shrinkage of the mycelia in vitro, and the disruption of spores in UVC -treated potatoes. Moringa leaf extracts were prepared and adjusted into different concentrations, MLE 1%, MLE 1.5%, MLE 2%, MLE 2.5%, and MLE 3%. These concentrations were evaluated for their efficacy against F. solani in vitro and in vivo. The findings demonstrated that MLE 1.5%, MLE 2.5%, and MLE 3% inhibited the mycelial growth of F. solani by ≥ 50% in vitro. The in vivo findings revealed that both MLE 2.5% and MLE 3% reduced incidence of dry rot in potatoes. The antifungal activity of moringa was increased at higher concentrations. The scanning electron micrographs showed mycelia distortion in samples treated with moringa and the disruption of F. solani spores on the treated potatoes. It also indicated the formation of biofilms in moringatreated potatoes. Furthermore, this study evaluated the effect of integrated control of F. solani using UVC and moringa leaf extracts. The in vitro results demonstrated that samples treated with MLE 2.5% and exposed to UV-C for 15 minutes inhibited the mycelial growth of F. solani by 100%. ‘Sifra’ potatoes exposed to UV-C for 15 minutes and treated with MLE 3% had the lowest disease incidence (8.33%). The scanning electron micrographs showed abnormal, shrinkage, disruption, aggregation and reduced hyphae length of mycelia in samples treated with both UV-C and MLE. Moreover, it indicated the formation of biofilms in UV and moringa-treated surfaces of potato wounds. These integrated treatments enhanced efficacy compared to the individual application of either treatment. UV-C can be integrated with moringa and be used as alternatives to synthetic fungicides to control dry rot of potatoes.
Investigating the utilization of indigenous forestry as a pathway for commercial forestry, community upliftment and land restoration.
(2024) Mathenjwa, Kuhlekonke Khulani.; Mbili, Nokwazi Carol.; Burgdorf, Richard.; Laing, Mark Delmege.; Sardeshpande, Mallika.
Forests play a vital role in sustaining ecological balance and providing essential resources for human well-being. In South Africa, forestry has predominantly relied on non-indigenous tree species, leading to limited natural forests and an increasing dependence on commercial forest plantations. These plantations are mainly made up of commercial exotic monocultures constituting pine, wattle, and eucalyptus species. Some of these exotic species tend to colonize the natural environments of local indigenous species and grasslands where they ultimately alter the soil and water conditions to outcompete local species. In addition, due to their greater growth forms than indigenous tree species, they alter the structure of natural vegetation which negatively impacts nutrient cycles and water availability. As a result, the need to explore alternative approaches in forestry that prioritize indigenous tree species has become evident. While indigenous commercial forestry is practiced globally, South Africa has untapped potential due to the limited number of indigenous tree plantations in the country. To explore the use of indigenous trees, the main aim of the project was to investigate the use of indigenous trees for commercial forestry, community development, as well as land restoration by assessing and evaluating the growth and survival of indigenous species through the application of propagation methods and the incorporation of plant growth-promoting fungus Trichoderma asperellum (Eco-T). This was followed by assessing ecological benefits of indigenous trees such as biodiversity conservation, soil nutrient analysis, and evaluating cost-effective methods and market potential for indigenous tree propagation, as well as the recovery of trees in anthropogenic soils. This aim was firstly achieved by assessing the feasibility and potential of indigenous forestry in South Africa through a literature search and then further reported on indigenous tree species' importance and utilization along with their associated resources. Subsequently, this research investigated the utilization of indigenous tree species in South Africa, particularly within three peri-urban communities of the eThekwini municipality, KwaZulu-Natal. The first phase of sampling followed snowballing sampling strategy through assistance from local authorities (N=29), and a questionnaire was administered at one of the focus group discussions (N=10). The second phase of sampling used purposive sampling strategy to identify interviewees (N=10). Ethnobotanical data was collected and a total of 21 indigenous tree species were identified and reported across the three communities, emphasizing the utilization patterns and preferences of local species. Amongst the reported species, 12 species were utilized in either all three or two communities. Across all three sites, four indigenous tree species emerged as the most commonly utilized species, notably, Sclerocarya birrea, Prunas africana, Trichilia emetica and Ficus sur, accounting for 90% of participants (n=20). Fruits and medicinal products derived from bark and leaves were the most commonly utilized resource products from indigenous trees, constituting 60% of overall usage by participants. These findings highlighted that indigenous tree species with multiple uses were commonly utilized more than those species with one use, which elucidates the commercial value and economic potential of those. Treepreneurs emerged as pivotal components in this study that showcased profound knowledge and commitment to indigenous tree propagation and cultivation, expressing a clear preference for indigenous species over alien invasive plants. Hence, understanding the perspectives and needs of the local community is essential for the successful implementation of indigenous commercial forestry. The growth of indigenous tree species under field and greenhouse conditions was assessed. A total of five indigenous tree species namely Trichilia emetica, Harpephyllum caffrum, Sclerocarya birrea, Ficus sur and Canthium inerme were selected for this study based on the preliminary findings of the ethnobotanical survey. Tree seedling growth and survival were the important parameters evaluated in this study to investigate the impact of Trichoderma asperellum (Eco-T) on the growth of indigenous tree species. Noteworthy results obtained from the field growth establishment trial include the highest survival rate H. caffrum and the fastest growth in F. sur, accounting for 100% and 33.13 cm, respectively. However, the application of Trichoderma treatment did not have any significant impact on the growth and survival of the indigenous tree species. These findings lay a great foundation for the cultivation, survival, and growth of indigenous tree species under field conditions. Greenhouse cultivation of indigenous tree species was conducted using anthropogenic soils from degraded lands. Here, the growth forms of indigenous tree species compared to the exotic species Eucalyptus grandis were investigated. The application of Eco-T as a treatment was also examined on the survival and growth of the seedlings. Indigenous tree seedlings exhibited a high survival percentage except for S. birrea in both Eco-T treated and untreated samples, accounting for 67 and 92%, respectively. Notably, the overall highest change in growth of height was observed in seedlings of F. sur with 48.8 cm but not as high as that of the control sample accounting for 106.16 cm. However, the treatment did not have any significant impact on the growth and survival of indigenous tree species. These results highlight the potential expressed by indigenous tree species especially F. sur under field and greenhouse conditions, in forestry and land restoration. They further emphasize the need for the development of specific indigenous tree species of commercial and ecological value. Furthermore, this study investigated the effect of different rooting hormones in the growth of different indigenous tree species from stem cuttings and then assessed the feasibility of propagating indigenous tree species using cuttings. In this study, four treatments namely Seradix, Dip n Grow, Eco-T and control were tested on three cutting types of the five indigenous tree species. All treatments showed no significant impact on the survival and growth of the species. At the end of the growing period, only one out of five species had survived, sprouted and rooted, accounting for 16% of F. sur. High mortality was observed at the end of the growing period (12 weeks) and can be accounted by various factors such as oversaturation on growing medium, temperature, and moisture. The findings revealed to yield great propagation success, compatibility of rooting hormones, type of species and cutting type must be taken into consideration. The findings further reveal the slight feasibility of propagating indigenous tree species from stem cutting, but also express great potential for F. sur. Hence, more research and development are needed to explore the potential of F. sur as well as other important indigenous tree species that can add value in forestry and be utilized for commercial purposes. Lastly, this study could provide valuable information for forestry managers, researchers, and policy makers to support the conservation and sustainable management of indigenous tree species. Overall, it can serve as a blueprint for similar initiatives and can be applied in various contexts advocating for a more inclusive, ecologically sound, and sustainable approach in the forestry sector.
The evaluation of the effect of biological control agents and melatonin against fusarium oxysporum infecting potatoes.
(2023) Mbatha, Londeka Akhona.; Mbili, Nokwazi Carol.
Potatoes (Solanum tuberosum L.) are essential to the South African agricultural industry. Postharvest diseases, including Fusarium dry rot (FDR) caused by Fusarium oxysporum (S.), are detrimental to the potato industry, resulting in yield and economic losses. Currently, fungicides are the primary means of controlling the disease commercially. However, the use of synthetic chemicals has reduced their efficacy against some Fusarium strains. Therefore, there is a need for safer, more sustainable, and environmentally friendly control methods for the management of postharvest fungal diseases such as FDR. Biological control agents (BCAs) and generally regarded as safe (GRAS) products have inhibitory effects against various pathogensand can be used as alternatives to synthetic chemicals. The aim of the study was to evaluate the efficacy of biological control agents (yeast and bacteria) and melatonin, individually and in combination, against F. oxysporum in vitro and in vivo. To evaluate the efficacy of the potential BCAs, 30 isolates were obtained from the exocarps and leaves of various crops, namely, potatoes(Solanum tuberosum), sweet potatoes (Ipomoea batatas), erect prickly pear (Opuntia stricta), Ganoderma mushrooms (Ganoderma resinaceum, Ganoderma austroafricanum,) and tomatoes (Solanum lycopersicum). The isolates were screened against F. oxysporum using the streaking method. Isolates NG1, NG2, NG3, NG4, and KG1 inhibited the growth of F. oxysporum on potato dextrose agar by more than 50% and were selected for secondary screening. In the secondary screening, isolates NGI (60%) and NG2 (62%) significantly inhibited mycelial growth of F. oxysporum on PDA compared to the control. In vivo, isolates NG1 and NG2 significantly reduced the severity of FDR on inoculated ‘Sifra’ potato tubers and had disease severity percentages of 47,2% and 46,1%, respectively, compared to the untreated control. BLAST prediction identified isolate NG1 as the bacterial species Burkholderia cenocepacia (strain LMG 16656) and isolate NG2 as Bacillus amyloliquefaciens (strain MPA 1034). The efficacy of melatoninwas determined by screening six concentrations (0 M; 1 M; 10 M; 15 M; 50 M and 100M) of the phytohormone against F. oxysporum using the disc fusion method. The best- performing melatonin concentrations were selected for secondary screening and progressed to in vivo screening. Melatonin concentration of 100 M had the highest inhibition percentage (40,83%) of F. oxysporum in vitro compared to the untreated control. The second and third best concentrations were 15 M and 50 M with inhibition percentages of 35,83% and 34,17%, respectively. The efficacy of melatonin as an antifungal agent, was significantly lower in vitro compared to the in vivo results. In vivo, the ‘Sifra’ potato tubers treated with 100 M showed the lowest FDR severity of 58,57%, followed by 50 M and 15 M with disease severity percentages of 59,54% and 60,31%, respectively. Subsequently, the effects of the integration of best-performing BCAs and melatonin were evaluated. BCAs, (Burkholderia cenocepacia and Bacillus amyloliquefaciens) were integrated with six melatonin concentrations and screened against F. oxysporum in vitro and in vivo. In vitro, treatment Bamy + MEL100 had the highest mycelial growth inhibition percentage (59,92%), followed by Bamy + MEL15 and Bamy + MEL50 with mycelial growth inhibition percentages of 56,12% and 55,27%, respectively. ‘Sifra’ potato tubers treated with treatment Bamy + 100 M melatonin had the lowest disease severity of FDR of 50,61% compared to control treatment after 9 days at 25℃. Bcen + 100 M melatonin and Bamy + 50 M melatonin exhibited the disease severity percentages of 52,63% and 59,72%, respectively. Overall, tubers treated with a combination of melatonin and B. amyloliquefaciens showed less severe symptoms of FDR across all concentrations. Furthermore, the effects of the exogenous application of B. amyloliquefaciens and melatonin on the quality parameters of the potato tubers were evaluated. The treatments were administered to tubers using the dipping method and stored at ambient temperature for 14 days. The treated tubers were sampled and prepared for phenolic, protein, and ascorbic acid determination assays. The exogenous application of 100 M melatonin combined with B. amyloliquefaciens was the most effective treatment with the highest phenolic content (144,1 mg GAE/g DW), and protein content (68 mg/g DM). Tubers treated with melatonin had the highest ascorbic acid content (5,48 mg AAE/100g DM). Findings indicated that the exogenous application of melatonin and B. amyloliquefaciens do not have adverse effects on the quality parameters of potato tubers. This study demonstrated for the first time, the efficacy of melatonin as an antifungal agent against F. oxysporum causing FDR on potatoes and the effectiveness of the combination of melatonin and the antagonistic microorganism, B. amyloliquefaciens against F. oxysporum.