Soil-borne pathogens have the potential of destabilizing the food security in the world if not properly controlled. One such pathogen is Spongospora subterranean (Sss) the causal agent of powdery scab disease that can severely reduce the quality and marketability of potato tubers. Sss reduces tuber yield, by disrupting root function (water and nutrient uptake) in actively growing potato plants, and causes severe galling on roots. Despite the substantial amount of research on management options for Sss on potatoes, no single measure is available for its effective control. Control strategies, including cultural management, host plant resistance, and the use of chemicals have been tested with limited success.
Set against this background, different potential management strategies that are environmentally friendly and sustainable are being explored to ameliorate the devastating effect of Sss on potato crop. Proposed future recommendations on effective management are mainly based on an integrated pest management approach (IPM) with the use of antagonistic soil microorganisms earmarked to contribute a substantial and sustainable component. Research to investigate chemical and microbial communities associated with Sss suppression has been proposed at the University of Pretoria with the goal of identifying strains or chemical compounds that can be used for biological control of the pathogen.
To that end, the proposed project has three main objectives (i) to compare rhizosphere and glucosphere microbiome community of infected potato and healthy potato from different agro climatic regions in South Africa, (ii) to isolate potential biological control agents and microbial targets for soil augmentation and (iii) test the most promising ones, using the microencapsulation method, for their efficacy in greenhouse experiments and in field trials.
The first two objectives have a basic research value being devoted to reveal potential microorganisms that play a crucial role in Sss suppression. The third objective, involves the isolation and characterization of natural biocontrol agents against Sss, it follows an idea-to-application research scheme that promoting lab-to-market approach. The long term vision of this project is to develop integrated pest management systems that incorporates traditional and novel approaches including biological controls and other management practices to address the farmers’ needs for safe, sustainable and cost-effective management of potato pests
Project design and implementation
The first phase of the project consists of collection of samples from commercial potato fields with powdery scab infection. Soil samples will be taken from the rhizosphere and geocaulosphere of Sss infected and non-infected plants as well as bulk soils. Microbial DNA will be extracted and processed using Next Generation Sequencing (NGS) technologies and processed with different software for the enrichment, network and functional analysis. For specific OTUs, blastn searches will be done to look at sequence identity with known biocontrol strains.
The second phase will be the development of potential biocontrol agents for Sss.A collection of culturable putative biocontrol agents will be generated and screened in vitro for antimicrobial features against Sss and then in planta for their ability to control the pathogen. Different methodologies of inoculation will be tested: seed and/or root submersion, spray and microencapsulation (coating of biocontrol agent with a biodegradable polymer to ensure a slow release of the bacteria in the soil by pore-assisted diffusion or degradation of capsules). This last method in particular is very promising since encapsulated bacteria will be released in the plant-soil microenvironment slowly and continuously and they are expected to possess an extended shelf life at different environmental conditions.
To get the idea started and considering the broad nature of the research, a multi-disciplinary team that includes a microbial ecologist, molecular biologist, plant pathologist and soil scientist will be involved in the project design and implementation. This work has the potential to produce results with direct impact on biocontrol agents development programs and will provide transferable skills and knowledge to the agricultural industry. Therefore, in addition to scientist, other stakeholders will include farmers, pest control advisors, biopesticide industry and the public.
Positive scientific and socio-economic impacts
Foremost, the proposed research will facilitate transition from over reliance on chemical insecticide usage by providing effective and environmentally-friendly alternatives. At a minimum, results from the project will be integrated into existing IPM programs for management of Sss without negative human and environmental risks, and by providing the public with food containing lower levels of synthetic chemical residues. Economic opportunities will be created by enhancing the commercial aspects of biological products, which will have a multiplier-effect on other sectors in the value chain. The project will bring about a reduction in yield losses of potato due to Sssdiseases and improve profit for commercial growers and ensures food security through increased in yield per unit of cultivated land.
My long term vision is an integrated platform of addressing farmers’ needs for pest management that leverages and incorporates novel approaches including traditional methods, biological controls, and resistant varieties for management of diseases. This system looks at environmental sustainability, on the use of biocontrol agents that are expected to become established in the ecosystem and keep target pest populations below damage thresholds, requiring little-to-no farmer investment in the long term. Thus, these biologicals will benefit a diversity of potato farmers, independent of farm size. In addition, for women farmers, with generally lower asset levels and less access to information and inputs, biological control will be particularly valuable, for providing an economically viable option for improving potato protection in a sustainable and environmentally friendly way.
Norman Muzhinji, South Africa