By David Arome
How pioneering microbial research to develop a biocontrol Agent was designed to tackle leaf and fruit diseases to reduce losses in the South African fruit industry
Every year, the world grapples with staggering losses of 1.3 billion tonnes of food after harvest — and nowhere is the crisis more urgent than in Africa. About 52% of fruit and vegetables produced in Africa are wasted during handling and storage, due to a lack of effective refrigeration, cold chain and distribution systems, transportation and inadequate storage facilities.
Compounding this issue, leading fruit-producing countries like South Africa suffer economic losses from fungal pathogens caused by for instance, Penicillium spp., Botrytis cinerea, and Alternaria spp., which can infect preharvest and cause decay during distribution and retail.
To tackle these microbial threats, Professor Lise Korsten, a distinguished plant pathologist at the University of Pretoria and President of the African Academy of Sciences, provided deep insights in an interview into her research, particularly in developing microbial antagonists — helpful organisms that stop harmful pathogens from infecting plants and causing losses — to manage postharvest diseases in fruit.
Significantly, Professor Korsten research is often cited as pioneering in Africa for introducing South Africa’s first commercially available microbial biological control agent (BCA), for leaf and fruit diseases to control losses and waste in the food system, notably in the avocado and mango industries.
This scientific innovation is important, especially considering that One fifth of the world’s hungry live on the African continent, as revealed by UNICEF’s 2024 report. The figure is especially alarming in a region of abundance, where vast proportions of food never make it from the farm to the table. Pre- and postharvest losses not only undermine food security but also erode farmers’ incomes and strain national economies.
In response to this long-standing challenge, Professor Korsten’s research continues to drive innovative, science-based solutions by harnessing naturally occurring microorganisms as BCAs to reduce fruit losses and transform agricultural outcomes across Africa.
Agriculture traditionally relied heavily on agricultural chemicals. It was a different world then—using effective chemicals regularly was the normal practice. For export-oriented farmers, effective postharvest chemicals were essential to retain quality while the fruit was in transit to foreign destinations for extended periods of time. Pushing self-life was essential to being competitive in these markets, which often required 42-day transit periods. Today, most of them are no longer registered, and their negative impacts are detrimental to the environment.
Nonetheless, “Though chemicals are effective, they must be used responsibly to avoid a downstream harmful impact on the environment, spray operators and consumers. Agricultural chemicals are thus valuable to protect crops and support plant growth if used correctly, i.e. applying the correct spray dosage at the best time, considering the withholding period before harvest and following good agricultural practices for correct storage and disposal of containers and obsolete products.” Professor Korsten reveals.
Consequently, biological control evolved as a more environmentally friendly alternative, and is used as an integrated strategy, and is one of the biggest evolving study areas, especially seen as part of the growing green economy. Many researchers are now developing biological agents—mainly bacteria or fungi—that are specially formulated for application via drones or using standard spray equipment to protect plants and boost their growth. This concept is similar to the use of beneficial microbes (probiotics) used after an antibiotic course to protect the human gut microflora that regulates digestion, immunity and overall health. The science around the microbiome of the human gut is currently a major focus area and is studied in connection with brain health and many other key diseases. Scientists are now also focusing increasingly on the use of natural antagonists and understanding the plant microbiome for plant health and plant growth-promotion (PGPR).
In this context, Professor Korsten explained that “It has become increasingly important to understand plant cell-host and microbe level to understand host defence mechanisms and how to regulate consortia of organisms to achieve more durable disease control. From this, we can identify the core microbes present on the plant and how they interact with both beneficial and harmful organisms. This has completely transformed the way we approach disease control to ensure sustainable shifts in population dynamics.
To that end, “We must empower scientists with access to these modern technologies, proper training on how to use them, and support the further development of natural bioproducts. These efforts can open new job opportunities—enabling agricultural scientists to start initiatives, selling these products, advising farmers, and registering to become a plant health practitioner and work as a consultant.” Professor Korsten said.
Building on that and looking at the advantages, Professor Korsten noted that biological control agents or BCAs possess special benefits as natural plant inhabitants often contribute to a stable microbial balance in the plant environment, providing more effective disease control. BCA’s, leverage their natural ability to live on plant surfaces, interact and outcompete other intruder organisms and protect ecological niches, rendering a natural eco balance on the plant that prevents intruder pathogens from establishing, infecting and causing plant diseases. BCA’s can contribute to retaining a healthy crop, good yield and reduce losses and even food waste at the end of the supply chain.
However, “While chemical fungicides are effective, there is an increasing concern about possible buildup of pathogen resistance, pesticide residues, and the environmental impact. What is also important is correct storage, application and destruction of empty chemical containers and compliance with not using any unregistered or illegal products”. Professor Korsten indicated.
As a result, fresh produce containing above allowable levels of chemical residues may not be sold to the public. This is effectively regulated for export produce, but not always for local and most certainly not in the informal sector. Continued exposure to high levels of pesticide residues may have a serious long-term health impact and has reportedly been associated with certain diseases such as Parkinson’s increased cancer risks etc.
Biological control is therefore an important piece in the puzzle of plant health, ensuring less reliance on pesticides and providing a more environmentally friendly holistic approach, ensuring that the post-harvest crops stay safe and remain protected.
In explaining this further, how the BCA work to control postharvest losses, Professor Korsten noted, that every biological control organism works in its own unique way. Some organisms even have more than one mode of action, switching between them over time.
“At times, you want the biological agent to grow quickly—especially when it’s competing with other microbes—so it can take over space. In other cases, you want it to produce secondary metabolites—compounds that can be released and directly kill the pathogen. Or it might produce volatiles that affect the pathogen in other ways. Often, it’s not just one method—we look at combinations of different actions to get the best results.” Professor Korsten said.
Moreover, Professor Kosten explain “Microbial BCAs target a wide range of plant pathogens, and the ones we focus on often depend on the crop and the part of the plant we want to protect. For example, in some regions, we deal with root diseases caused by Fusarium oxysporum or fruit diseases caused by Colletotrichum spp. Whether it’s the leaf, fruit, root, or stem, we select pathogens based on the specific threats to each part of the plant.”
The biggest problem with research, professor Korsten noted, in the laboratory, you can isolate, identify and maybe test it in the greenhouse and may have good results. Immediately, you go commercial. It’s a different ball game because there are many environmental conditions that can affect the research
A survey conducted over two decades ago on BCA shows that some farmers did not originally believe in using these products but today this narrative has changed, and farmers are increasingly using BCAs as an effective crop protectant.
The field of biocontrol is now well established, and many successful products have been launched and profitably commercialised, based on credible research and effective industry adoption. Scientists working globally are also increasingly connecting and incorporating scientists from various African countries like Uganda, Tanzania, and Kenya, who support the development of their unique BCA’s. “Each country has the potential to create its range of natural products, rather than relying on a one-size-fits-all solution. The focus should therefore now shift to empowering more local development, innovation and adoption of this technology for safer, healthier food for all.” Professor Korsten hinted.
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