3. Electronic Theses and Dissertations (ETDs) - All submissions
Permanent URI for this communityhttps://wiredspace.wits.ac.za/handle/10539/45
Browse
1 results
Search Results
Item The impact of organic compost on the infectivity and virulence of entomopathogenic nematodes and their bacterial symbionts as biocontrol agents(2019) Khumalo, Nolwandle NolenA safer and greener alternative to chemical pesticides includes the use of entomopathogenic nematodes (EPNs) and their endosymbiotic bacterial pathogens as biocontrol agents. Entomopathogenic nematodes of the genera Steinernema and Heterorhabditis cause disease in insect pests, killing them within 48 hours, with the help of their highly virulent insect pathogenic bacterial symbionts belonging to the genera Xenorhabdus and Photorhabdus, respectively. The efficacy of EPNs in the field is affected by abiotic and biotic factors, thus understanding the soil ecosystem and its interaction with EPNs will aid in improving the application of EPNs in many agricultural soils post application. The research project focused on isolating and identifying locally adapted EPNs and their bacterial symbiont isolated from the North West province in the Magaliesburg region. Investigating factors affecting the survival, virulence, and persistence of EPNs in the soil, by the use of adding soil amendments such as organic compost namely mulch, organic compost, professional potting mix, organic lawn dressing mixed with loamy soil and coarse river in soils undergoing progressive dehydration. The effects of different soil composition on the behaviour and host-seeking efficiency within the soil profile and EPN response to desiccation tolerance was also investigated. EPNs were retrieved and harvested using the soil baiting technique with Galleria mellonella and White trap method respectively. PCR amplification of the 18S rDNA and 16S rDNA sequencing of the PCR amplicon was used to establish the phylogenetic affinities of EPN isolates and their bacterial symbiont using GenBank sequence database respectively. The presumptive Heterorhabditis species and Steinernema species isolated were found to show high affinity to H. bacteriophora (MG334257.1) and S. khoisanae (MH697401.1) respectively. The symbiont bacteria only isolated of H. bacteriophora was identified as Photorhabdus luminescence subsp. laumondi (KT963833.1). The use of organic compost did not have any detrimental effect on EPNs. The Mulch soil amendment resulted in the highest insect mortality rate across different application concentration (mass: mass basis) when mixed with loamy soil. It was observed that virulence and efficacy decreased over 7 days of progressive dehydration. In soil profile larvae locating behavioural studies, H. bacteriophora was found to be a cruise predator (search and forage) in search of a new host. Soil composition affected host locating ability of H. bacteriophora infective juveniles (IJs). H. bacteriophora IJs were able to survive desiccation tolerance with resuscitation by rehydration with water for a period of 8 weeks however infectivity and survival of IJs to locate the host were affected. Overall the type of compost used based on its feedstock iii composition, the concentration of nutrients and organic matter mixed with a specific type of soil texture had a significant effect on the infectivity and survival of H. bacteriophora IJs in the soil. In conclusion soil physical structures affects EPNs infectivity post application and the knowledge obtained will be used to improve soil application strategies and formulation products so that EPNs can be used as commercially viable biocontrol agents.