By Lize Reinecke
The photo is provided by Weebly .
With the continuously growing human population, food and fodder are on increasing demand. Plant pathogens like bacteria and fungi are major threats to food security, and over the history of mankind many different solutions to controlling them has been tested (Mérillon and Ramawat 2012).
Synthetic control of pathogens, like the use of chemicals has great impact on the environment, and the effect on human health. Synthetic control measures also have pathogens that develop resistance against it (Cui et el. 2019). Due to this negative impact, alternative control measures like biological control is sought after (Mérillon and Ramawat 2012). Biological control is the destruction or inhibition of pathogens by other pathogens (Agrios 2005). Some of the species available to use for biocontrol purposes are Bacillus, Metarhizium, Pseudomonas and Trichoderma. In some circumstances, biological control agents even result in a higher crop yield than when the pathogens are treated with any other method (Cui et al. 2019) and also makes for a more sustainable agricultural future (De Silva et al. 2019).
Biocontrol agents are not only a more sustainable option, but it has other advantages as well. Some of these include their faster decomposition and lower toxicity to non-target species. Because they have various mode of actions, they are also more efficient against pathogens that are prone to develop resistance against synthetic pesticides (Marin et el. 2019).
This species inhabits a large variety of environments which are ideal since it can be applied in different ecological niches to target a variety of plant pathogens (Fira et al 2018). This bacterial species is present in air, soil, water and the rhizosphere (Connor et al. 2010), and can produce antimicrobial compounds and secondary metabolites (Stein 2005). Some of these antimicrobial compounds are compounds such as lipopeptides which has an inhibitory effect on the growth of plant pathogens (Wu et al. 2019).
Bacillus velezensis are the most common bacteria used as a biocontrol agent (Cui et al. 2020). The production of three different lipopeptides by B. velezensis are the main mode of antimicrobial action. These three lipopeptides are especially active against plant pathogenic fungi (like Aspergillus spp. and Fusarium spp.) that produces mycotoxins harmful to animals and humans (Liu et al. 2019).
The bacteria Bacillus thuringiensis is also widely used as a biocontrol agent. This is because this specific species has crystal-producing strains which have insecticidal properties. This bacterial species can be used to control both air- and soilborne pathogens like fungi and other bacteria either by competition (Mérillon and Ramawat 2012).
Fungi are usually the culprits causing plant diseases, but it is not the case with Metarhizium spp. This is an entomopathogenic fungi which occurs in various habitats in different climates worldwide (Kryukov et al. 2019) and which is especially effective to use against grasshoppers. An entomopathogenic fungus colonizes and parasitize insects (Mérillon and Ramawat 2012).
Not only does this species of biocontrol fungi have a wide range of activity against various pathogens, but it also colonizes the rhizosphere, promotes plant growth and increase resistance to phytopathogens. The promotion of plant growth is due to the transfer of nitrogen from other dead insects to the plant, as well as rehabilitating nutrient deficient soil (Kryukov et al. 2019).
This fungus produces pathogenicity factors and chitinase which then breaks down the chitin walls within plant pathogenic insects (Francis 2019). It also has an enzyme which decomposes the proteins of nematodes acting as nematicides (Mérillon and Ramawat 2012). The number of spores needed to infect and kill 50% of an insect population within 10 days are only a 1000 (Mérillon and Ramawat 2012).
The bacterial species Pseudomonas fluorescens has only recently been discovered to have biocontrol characteristics. Controlling soil-borne pathogens has been a major problem throughout the years, but this new biocontrol agent might be the solution (Baehler et al. 2005). P. fluorescens are a siderophores, which causes this pathogen to have inhibitory effects on spore germination and mycelium formation (Abo-Zaid et al. 2020).
P. fluorescence has chloroform fractions which has significant activity against pathogenic bacteria and toxic fungi (Marrez et al. 2019). It is also a competitor for niche-based nutrients. This bacteria is, however, inconsistent in different environments so there us still a lot of research to be done on how to optimise the use of this biocontrol agent (Dutta et al. 2019).
Trichoderma spp. are usually used to control fungal pathogens like Fusarium wilts (Hewedy et al. 2019). This fungus as biocontrol agent can successfully colonise soil and survive in it for up to a year (Xian et al. 2019) and acts in vitro (Mérillon and Ramawat 2012).
The Trichoderma spp. used as biocontrol are known for its effectiveness since this fungal species colonizes and grows aggressively in soil (Hewedy et al. 2019). It also has other mechanisms to control plant pathogens such as hyperparasitism and competition. This fungal genus also triggers induced resistance in the host plant and can enhance plant growth (Xian et al. 2019). It also is a mycoparasitic species which can act against fungi, and it also has been characteristic to be used against airborne diseases especially when integrated with chemical control (Mérillon and Ramawat 2012).
By Amy Grundling
Photo by Annika van Zyl & Jaco Kruger
It was recognized, during the 2009 World Summit on Food Security, that food demand will increase with 34%-70% by 2050 (FAO, 2019). It is estimated that the population will increase to 9 billion people, causing an additional annual consumption of 200 million metric tons of meat and 1 billion metric tons of cereals for food and feed (Floros, 2010). To meet the increasing food needs, it is necessary for the agricultural sector to become more efficient and productive. Biotechnology provides the potential to support the increase of production and yield and to develop commodities that are richer in nutrients.
Since the first genetically modified (GM) organisms were introduced in the late 1980s, the debate arose whether gene technology is beneficial or detrimental to human health. However, the debate has failed to clarify an agreed direction of policy (Azadi, Hossein, 2010). The use of GMO’s has divided important stakeholders with conflicting opinions, while the public is left in the side-lines. Despite no scientific evidence published on the detrimental use of GMOs, activists in many countries have continued to fight against the use of GM crops. These groups state that safety, ethnical, religious and environmental concerns are more important than the benefits of increased productivity and improved nutritional value (Azadi, Hossein, 2010). Due to the uncertainty created by these groups, many developing countries have not planted any GM crops – because of the fear of biosafety (Azadi, Hossein, 2010). The new European Union regulations, requiring all GM products to be labelled, will further discourage the planting of GM crops in poor countries (Paarlberg, 2002).
The issue is the impact of international regulations on the food security in the developing countries. According to the Food and Agricultural Organization, approximately 820 million people remain malnourished, including at least 250 million children (FAO, 2019). Nevertheless, biotechnology provides the potential to increase yields and nutritional value of crops, which is vital for resource-poor and small-scale-farmers. Biotechnology can be used to genetically modify plant and animal species. For example, to increase the nutritional value of cereal grains and rDNA biotechnology can be used to increase the protein quality. With the increasing challenges developing countries face due to climate change, more resources are needed to produce food. By using drought tolerant crops, such as maize, it enables small-scale to adapt to the changing environment (Floros, 2010). The increase in yield and the shorter growth period in GM crops also decrease the use of chemical fertilizers and pest management, therefore improving cost efficiency.
The uncertainties regarding GMO’s have affected policy development and the publics opinion of the use of GM crops significantly. People fear the things which they do not know, it is therefore important that scientific research must be conducted to prevent further uncertainties regarding GM crops and to share these findings with the public. By educating the public and policy makers on what biotechnology is, it will eliminate any myths which prevents the use of GM crops. Biotechnology is an important tool that needs to be incorporated in developing countries’ agricultural sectors. Through the benefits of biotechnology, food security can be improved, especially in developing countries. This will not only reduce famine but also malnutrition globally.
Azadi, H., 2010. Genetically modified and organic crops in developing countries: A review of options. Biotechnology Advances, I(28), pp. 160-168.
FAO, 2019. Food Insecurity is More than Just Hunger. [Online]
Available at: http://www.fao.org/state-of-food-security-nutrition
[Accessed 3 May 2020].
Floros et al., 2010. Feeding the World Today and Tomorrow: The Importance of Food Science and Technology. Comprehensive Reviews in Food Science and Food Safety, 9, 572-599.
Paarlberg, RL., 2002. The real threat to GM crops in poor countries: consumer and policy resistance to GM foods in rich countries. Food Policy, 27, pp247–50.
By Amy Grundling
Fruit trees set more fruit than what they can structurally support or properly develop. This occur more often in trees that was not pruned during the previous season. The excessive fruit remain small due to increased competition for carbohydrates and other nutrients. This increased demand for carbohydrates weakens the tree, which makes it more susceptible to pests, diseases and water stress. Excessive fruit in one season can also cause the tree to have alternate bearing or limb breakage. Thinning the fruit is therefore necessary to prevent these problems.
Fruit thinning is the removal of certain flowers and fruitletts after fruit and natural dropping have occurred. The benefits of thinning immature fruits include:
There are two main thinning methods that are used, which include hand- and pole-thinning. Hand thinning is slower than pole thinning, but more accurate. Hand-thinning is when some fruits are removed to ensure the remaining fruits do not touch each other at maturity. Therefore, on short spurs only 2 to 3 fruits can be left. On long branches fruits that are double, small, disfigured and damaged fruits should be removed. Pole-thinning involves using a pole due to the size of the tree which is too large for hand-thinning. A cloth is attached to the tuber hose at the end of the pole, to decrease bruising of fruits and branches.
The amount of fruits that should be thinned depends on the species and the individual tree’s fruit load. Stone fruits such as apricots and plums are small, therefore they should be thinned 5 cm to 10 cm apart from the branch. Nectarines and peaches are larger fruit, therefore they should be thinned 7.5 cm to 12.5 cm. Unlike stone fruits, which produce one fruit per bud, pome fruits produce cluster fruits on one bud. Therefore, pome fruits need to be thinned so that one fruit per bud are available to develop. The overall rule is that for every 15 cm of branch there should be one fruit.
Thinning should be done at the correct time of season depending on the type of specie. The method and amount of fruit thinning is also determined by the species of the tree. Thinning is an important management practice in the fruit industry to develop a constant fruit yield every year of high quality.
By Amy Grundling & Renée Grundling
Photo taken by Amy Grundling.
Having your own vegetable garden may be a dream come true hobby or simply a way to reduce grocery costs and improve a quality way of life. Growing your own vegetables puts you in charge of what is entering your body. You decide what you want to grow, how you want to grow it and how you want to treat it with nutrients and pesticides. You can therefore decrease unwanted elements frequently used in commercial farming and increase the organic nature of your diet.
Given our current Covid-19 situation, a vegetable garden can become a sustainable and safer solution to obtaining fresh produce. Not only will you avoid contact with contaminated grocery stores, but this will also keep you busy in self isolation or quarantine. Gardening has many health benefits including improving your state of mind, wellbeing and developing a sense of place and responsibility in your home. You may even enjoy the sun, fresh air and birds chirping while you tend your garden.
South Africa is entering its Autumn and Winter months, an ideal time to plant various types of vegetables depending on your location in South Africa. One can use the information below (Seeds for Africa, 2020) as a guide:
Seeds for Africa, 2020. VEGETABLE PLANTING GUIDES. [Online]
Available at: https://www.seedsforafrica.co.za/pages/western-cape-vegetable-planting-chart-1
By Adelene van Zyl
Compost is decomposed organic matter, which aids in plant growth. Compost ensures that plants can easily absorb nutrients from the decomposed organic matter. It keeps your soil healthy and ensures that the soil contains all the necessary nutrients. It is therefore important to consider what you add to your compost heap to prevent over supply of one nutrient and under supply of another.
Composting is a cost-effective way to ensure healthy plant growth from a small garden to a commercial farm. However, it is important to understand that generating compost from a sustainable compost heap will take time. Give yourself a time-span of one year for the compost heap to fully become sustainable and generating good quality compost.
How to structure a compost heap:
You can use any large container, depending on how much compost you want over a long period. The type of container is also not set. However, do consider limitations of materials and modify your container accordingly. If you use a plastic container, ensure holes on the side for aeration. If you use a wood container, ensure holes underneath to allow water penetration and preventing rot. The principle of making a sustainable compost heap is to use what you have.
Layers of a compost heap:
There are different methods one can use to determine how many layers should be in the compost heap and what plant materials you should use in each layer. The following is a basic example and should be altered according to what you have available.
The first layer is your ‘browns’ which consist of branches and leaves which already appear brown. This can be divided as separate layers as well. Examples are mulch from a chopped tree, old branches and leaves.
The second layer is your ‘greens’ which consist of freshly cut grass, fruits and vegetables. This is the layer where you can use any plant-based material. Examples are fruit and vegetable peels, rotten fruits and vegetables, used coffee or tea bags and eggshells. Make sure that no yeast-based products are added in the compost heap, as this will cause mold growth and ruin the whole compost heap.
The third layer is soil or manure. This layer need not be as thick as the other layers, but it is necessary to optimize the breakdown of the other two layers. You can add these layers on top of each other as indicated on the figure.
How to take care of your compost heap:
It is important to water the compost heap at least once every second week. This will aid in the breakdown of organic matter. You should also mix your compost heap at least once a month to ensure proper breakdown of the plant material. If you want to speed up the process, you can add compost activator as indicated on its package. Compost activator is usually added once one set of the three layers are present or when there is a large amount of browns relative to the greens.
By Lize Reinecke, Amy Grundling & Adelene van Zyl
Fertigation is the process of nutrient application through irrigation where nutrients are introduced to the watering system used for irrigation. Fertigation can be applied either through a drip or a spray irrigation technique. It is used to regulate the amount and duration of fertilizer application, the dilution of the fertilizer in the water as well as the start and ending times of the fertigation process.
In the nursery industry fertigation has become increasingly popular due to the high efficiency rate. Most growers use injectors to mix concentrated fertilizer solution into the irrigation system. A large variety of injector are available to meet the different needs of any size nursery. Well-designed systems can be monitored at different stages in the process to ensure that the injectors work efficiently and that the plant receive the correct amount of nutrients.
The nutrient solutions are prepared in stock tanks from where it is injected into the irrigation water tanks. For fertilizer to mix with irrigation water, the fertilizer must be at a higher pressure than the irrigation water, that is why it is referred to the fertilizer being injected into the irrigation water.
Types of Fertigation
There are four categories into which fertigation can be placed: Continuous, Three Stage, Proportional and Quantitative Application. The choice will depend on crop response and the risk of excessive nutrient runoff.
Advantages and Disadvantages
The advantages of fertigation include the precise control of both the concentration and balance of nutrients, an equal distribution of fertilizer, increased penetration of fertilizer in soil, decrease in nitrogen loss and nutrient solutions can easily be customised for any plant growth stage or species. Disadvantages of fertigation include high levels of toxicity in the irrigation system which can damage nursery crops and the environment, frequent mixing and applying of liquid fertilizers increase labour cost, clogging of irrigation pipes and exposure to high levels of fertilizer may result into health problems.
Fertigation can be applied from a small nursery to large commercial farming. This method enables farmers to lower their input cost through precision farming and maximise their production. However, it is important that fertigation systems to be monitored and managed frequently to prevent any damage.
By Amy Grundling
Sunburn is a physiological disorder that occurs on fruit species, such as apples, due to excess exposure of sunlight . This disorder causes large crop losses of up to 50% of the total crop yield in the South African apple industry . Depending on the type of cultivar, the symptoms of sunburn can vary from dark brown spots to white patch discoloration. The affected areas also create an easy entrance point for pathogens, causing the internal quality of the fruit to decrease. This combination results in decreased quality making the fruit unmarketable. Therefore, it is necessary to understand the causes of sunburn and how its effect on apples can be mitigated.
Types of Sunburn
1. Sunburn Necrosis: creates a brown or black necrotic spot on the fruit surface. This type of damage occurs when the fruit surface temperature reaches 52 ± 1◦C for ten minutes and longer . The high temperature of the fruit surface causes the denature of proteins, which decreases the integrity of the membrane. Damage can occur between a few millimeters to numerous centimeters deep in the sub-epidermal tissue. These symptoms will be visible after one to four days after exposure.
2. Sunburn Browning: is the most common type of sunburn that affects attached apples that are exposed to the sun. This type of sunburn causes brown, yellow and bronze spots on the exposed surface of the apple. The discoloration is due to the decrease levels of chlorophylls and anthocyanins and increased levels of carotenoids and quercetin glycoside in the surface . Sunburn Browning is a result of high solar radiation that increases the fruit surface temperature to a specific minimum temperature. Unlike Sunburn Necrosis, Sunburn Browning do not cause damage in the sub-epidermal tissue.
3. Photo-oxidative Sunburn: occurs on apples that have grown under the shade and then suddenly becomes exposed to solar radiation . This type of sunburn creates white patches on the surface of the fruit. These symptoms occur due to the fruit that are not acclimated to high solar radiation. The sudden exposure to sunlight can take place after thinning and pruning. The induction factors of Photo-oxidative Sunburn are the production of reactive oxygen species (ROS) and solar radiation in viable range of wavelengths; contrasting to Sunburn Necrosis and Sunburn Browning which is influenced by the maximum fruit surface temperature.
Indirect Factors that Influence the Severity of Sunburn
There are also many indirect factors that influence the severity of sunburn on apples. These factors include climate, geographic locations, previous exposure, soil, cultivar and crop cover. Low relative humidity with high temperature increases the atmospheric water demand. This causes higher levels of water stress, which increases the sensitivity of apples for stress-induced disorders. Wind velocity have an impact on the temperature of the air surrounding the fruit. Increased air movement reduces the heat by convection cooling. The susceptibility of the cultivars to sunburn also play a great role. Different cultivars have different susceptibility to sunburn due to the following factors: solar absorptivity, interception of solar energy, temperature tolerance, photostability, tolerance to UV radiation and the ability to acclimate. Cultivar such as Granny Smith and Jonagold are highly susceptible. Moderate susceptible cultivars include Fuji, Golden Delicious and Braeburn. The least susceptible cultivars are Pink Lady, Idad and Topaz.
The geographic location influences the probability of sunburn due to the elevation and latitude that impacts the climate of a specific region, as well as factors that influence the intensity of solar radiation such as aspect. South Africa have a combination of subtropical, arid and mediterranean regions. These regions experience clear summer skies, high temperature and high evaporative demand. This causes high levels of sunburn in the apple industry. Orchard management also play an important role in sunburn. Sunburn is more likely to occur in high-density orchard, for example. The fruit will be more exposed to solar radiation due to less canopy cover. Training system with open pruning also increases sunlight interception.
How to Prevent Sunburn
There are three main techniques, namely climate-ameliorating, suppressants and chemical, that can be used to decrease sunburn damage. Climate-ameliorating entails technological techniques that changes the micro-climate surrounding the fruit . Evaporative cooling is used to mitigate heat stress, through overhead sprayers. Heat is reduced through the evaporation, which decreases the fruit surface temperature. However, evaporative cooling does not reduce the damage done by UV radiation . Therefore, Sunburn Browning damage does not decrease under this system. The calcium and magnesium carbonates that are deposited on the surface of the fruit by water can also have a negative impact on the fruit appearance. Another downside of the evaporative cooling system is the high cost of installations, intensive management and high-water requirement. Due to these factors the South African apple industry do not use this system.
In South Africa shade nets are more frequently used. High-density polyethylene (HDPE) nets are placed over the tree canopy. The shade net reduces solar radiation interception experienced by the apples which in turn decreases fruit surface temperatures. The colour and density percentage of the material determines the effectiveness of the shade net. The downside of shade nets is the reduction of colour development in the red cultivars. However, the protection shade nets provide against excessive solar radiation and hail outweighs the negative effects.
Suppressants, such as particle films and sunscreen, are materials that are sprayed on the fruit. Particle films are composed out of kaolin clay, hydrated magnesium silicate or calcium carbonate . These white inorganic products reflect solar radiation from the surface of the fruit by increasing its albedo. The particle films wash of easily during the rain. Therefore, regular reapplication is necessary. Another drawback is the difficult removal of white residues from the calyx areas. This causes the fruit to decrease in market value due to health concerns. The sunscreen that is used on apple consist out of organic -chemical and physical inorganic particles . The sunscreen absorbs high-intensity UV wavelengths and then dissipated trough the emission of long wavelengths. Sunscreen needs to be reapplied periodically due to the rapid surface growth of fruit.
It is clearly seen that sunburn is a great risk for the farmers in the apple industry. It prevents farmers to export their products as international markets highly values visually and aesthetically appealing products. It is therefore important for South African apple producers to satisfy the consumers demand through by preventing sunburn on apples. South Africa have different climatic conditions, geographic properties and limited resources than other apple producing regions. It is therefore necessary for the South African apple producers to develop systems and use products that are specific for their needs. Through reducing sunburn, the 50% of yield loss can be prevented. This will not only decrease food waist, but also increase the farmers income through exports.
By Amy Grundling
Portulacaria afra, or otherwise known as the Spekboom, is an indigenous South African succulent plant. It has bright green small, round leaves with a red stem, creating a refreshing appearance. The average Spekboom usually grows 1.5-2m in hight. The natural habitat of the Spekboon is warm, arid and semi-arid areas, especially renown in parts of South Africa such as Ado Elephant Park and the town of Prince Albert.
The Spekboom is increasingly drawing attention for its unique characteristics and various uses. One of the most important characteristics is that the succulent is effective in carbon sequestration. By absorbing free carbon for tissue growth, the succulent decreases the amount of pollution caused by the burning of fossil fuels, acting as a carbon sink.
Spekbome is an ideal shrub to plant in a water scarce country such as South Africa. The succulent is a drought-resistant plant, which can survive on 250-350mm of water per year. Spekboom is easily propagated, which makes it an ideal plant to plant in your garden without spending money.
The following steps will show you how to propagate your own Spekboom:
Step 1: What you will need.
You will need the following list of products
Step 2: Select and prepare Spekboom cuttings.
Select a few healthy cuttings from a vigorous Spekboom, preferable in late spring. The ideal cutting should be between 10 and 15 cm in length. Look for vigorous branches with thick and healthy leaves. Make a 45° angle cut and remove the leaves at the end of the cutting.
Step 3: Dip the cutting in root growth hormones.
Moisten and dip the end of the cutting in a root growth hormone that will stimulate root growth. This step is not necessary, although it will increase the speed of the cutting’s root growth.
Step 4: Prepare a rooting pot.
Prepare a rooting pot that have several drainage holes at the bottom. Fill the pot with succulent potting mix or your own mixture of course and standard potting soil. Insert the Spekboom cutting into the soil and press lightly around the stem.
Step 5: Water the cutting.
Lastly, water the cutting and allow the soil to drain thoroughly.
Step 6: Watch it grow!
Place the potted cutting in indirect sunlight for at least five hours a day and apply water once a week. Rooting will take place within 14 to 20 days.
For more information, please visit the South African National Biodiversity Institute website:
By Renée Grundling
World Wetlands Day was celebrated on the 2nd of February, an annual day to celebrate the Ramsar Convention signed at Ramsar, Iran in 1971. South Africa was one of the first countries globally to sign the treaty. This year's theme is 'Wetlands and Biodiversity'.
There are currently more than 2300 designated Ramsar Sites, sites of international importance, all across the world. The above photo is one of the newest Ramsar Sites (no.2385), officially declared in September, 2019, and can be found in the Kgaswane Mountain Reserve, Rustenburg, South Africa. This wetland system is situated on a plateau in the Magaliesberg mountain range and has a variety of special characteristics including peat.
For more information go to https://whc.unesco.org/en/ramsar/.
In the following video, Dr. Piet-Louis Grundling discusses the importance of Wetlands:
By Adelene van Zyl
What is Sustainability?
Sustainability can be defined as the ability to be maintained at a specific level. It is important that the current generation should provide and maintain sufficient resources for future generations to live at the same economic and environmental level as the current generation does. In addition, sustainability entails maintaining changes in a balanced environment. The Earth has a certain carrying capacity in order to function at a good and healthy rate. When we exceed the carrying capacity of the Earth, we are no longer sustainable and put current and future generations at risk of depleting resources.
Sustainability is divided into three main components according to the World Summit of Social Development in 2005. The three components are economic development, social development and environmental protection. Sustainable development will only be effective if these components are interlinked. Sustainability will only attract investments if it promotes economic growth. By increasing economic growth, living standards in communities will be improved. In order for higher living standards to be sustainable, environmental protection and resource management must be applied.
The United Nations also saw sustainability as a key component in moving forward in unity, when 178 countries adopted Agenda 21 for Sustainable Development at the Earth Summit in Rio De Janeiro in 1992. There are seventeen Sustainable Development Goals in the 2030 Agenda of which ten out of these seventeen goals involve agricultural practices. These goals are:
Sustainability in Agriculture
The main goal of sustainability in agriculture is to meet the current food and textile needs without compromising future generations’ ability to meet their food and textile needs. Sustainability in agriculture aims to improve soil health, decrease pollution and to improve the use of water in farming practices. It also aims to increase crop quantity and quality in an efficient and effective manner, without degrading the environment.
In conclusion, I would like to encourage you with a quote from Arthur Ashe to apply sustainability:
“Begin where you are, use what you have, and do what you can.”