Most plant species can form a symbiotic relationship with beneficial mycorrhiza fungi. This partnership between the root and the fungus is called mycorrhiza, which literally means a fungus root. Dr Marianne Venter from Biocult, a company that produces mycorrhizal products, explains that the fungus’s mycelium, or filament, grows over and between the roots until it covers them.
The fungi not only expand the root area by 300% to 1 000%, but also stimulate root development. M ycorrhiza enhances the plant’s nutrient and water uptake, especially of phosphate and fixed phosphate. Plants, seed and cuttings treated with mycorrhiza are thus stronger, more resistant to diseases and are less vulnerable to environmental stresses such as drought, nutrient deficiency, flooding and wind damage.
Treated plants have thicker stems, indicating higher reserves. Dr Venter, however, warns that mycorrhiza doesn’t always result in higher yields. On grapes, nevertheless, it has been found to accelerate growth so vines reach the top wire of the trellis much faster than control subjects. ycorrhiza-treated plants in the same orchards also show more uniform growth than plants that have not been treated. But what does the symbiosis between the root and this beneficial fungus entail? First, the root signals its nutrient requirements to the mycorrhiza, which then specifically targets these nutrients, absorbing and transporting them to the root. These nutrients include phosphates, calcium, magnesium and micronutrients such as zinc, copper, iron, manganese and sometimes boron.
Studies on various crops have confirmed that farmers can cut their phosphate applications by 5% to 20% without compromising plant yield or quality, if mycorrhiza is used on crops that are planted in soil with a low level of plant-available phosphates, but high level of fixed phosphates. Utilising available nutrients more efficiently saves input costs and reduces the risk of environmental pollution through the over-application of fertilisers. Mycorrhiza has another benefit. network of mycelia can cover the roots to such an extent that it becomes increasingly difficult for root diseases such as pythium, phytophtera, and fusarium, as well as pathogenic nematodes to enter the plant’s root system.
The mycelia also secrete antibiotics that push these soil organisms away from the roots. It doesn’t kill the disease, but suppresses it. Dr Venter emphasises that she won’t use mycorrhiza as a curative measure if there are already huge problems with nematodes or root diseases. should rather be used as a preventative measure that helps to strengthen the plant and make it less vulnerable to attacks. “There’s very little mycorrhiza can do if a high pathogen population is already in the plant’s root zone before mycorrhiza is established,” she says. mycorrhiza performs well when applied with trichoderma, another type of beneficial fungi.
Trichoderma grows all around the mycorrhiza mycelium on the root, almost like a blanket, and attacks and destroys pathogenic fungi. Thus the trichoderma protects the roots and the mycorrhiza during the first few weeks of establishment, until the mycorrhiza is sufficiently established to protect the roots itself. Trichoderma produces spores around three months after establishment, depending on environmental conditions. By then, the mycorrhiza has formed such a thick net around the host’s roots that it’s almost impossible for the pathogens to penetrate it. If established and treated correctly, mycorrhiza will still be present in the roots of a tree 20 years later.
Mycorrhiza occurs naturally in the soil and is usually abundant in virgin soils. Dr Venter points out that certain cultivation practices, such as fumigation, monoculture and the excessive and long-term use of fertilisers, fungicides, herbicides and pesticides all adversely affect the presence and abundance of the fungi. Virgin soils will contain viable spores, but these practices can deplete them. Farmers should strive to put viable spores back into the soil. Spores vary in colour from cream to red and black.
“The lighter-coloured spores are more viable,” explains Dr Venter. “Light brown, red or cream-coloured spores have the greatest probability of germinating. In general, black spores are a bad sign, as they’re usually dead or dying.” There are various strains of mycorrhizal fungi. Farmers should therefore make sure they’re using a strong strain that provides the most benefits to the plants. Dr Venter prefers to use a mixture of at least four different species, as the diversity helps to ensure survival. The different species thrive under different conditions and at different pH levels, and the species also boost each other.
Mycorrhiza is believed to be effective on most plants and crops except for Brassica, rooibos and Proteaceae species. Dr Venter says that this is true in most cases, but it seems that mycorrhiza could form a beneficial relationship with these plants if they’re under stress. Positive results have been found with certain Brassica and rooibos species planted in seed trays or in areas where there are nutrient shortages, as well as with the production of some protea cuttings in nurseries. Some crops, such as blueberries and pines, also need a different type of mycorrhiza than the ones offered by Biocult. Contact Dr Marianne Venter on 083 3
Let Biocult establish your mycorrhiza
biocult offers mycorrhiza in three different products: a peat form, a granular form and a powder. The peat variant can be used with vine, shrubs and trees. granular form, which is dyed red so farmers can easily distinguish between it and pellet fertiliser, can be used in tunnels and in nurseries and is best suited for the production of vegetables, tomatoes, cucumbers and cuttings. he powder can be used to coat seed, together with a compatible fungicide or pesticide such as Flight, Raxil or Ingwe (Tebuconazole). Dr Venter says farmers prefer to obtain mycorrhiza-treated seed from agricultural co-ops as this saves time and effort.
Where plants are already established, the powder can be washed into the soil. “Due to the economy, in the case of sugarcane plantations, farmers should rather apply mycorrhiza after the first fell rather than during planting.” Dr Venter advises. She adds that some people wrongly think mycorrhiza can’t be washed into the soil at this stage. Mycorrhiza doesn’t necessarily have to be applied with each new plant or seed, as the fungal network can extend and form a symbiosis with the roots of other plants. This is ideal if you use green cover for mulching between permanent crops. “Some of our farmers sow mycorrhiza-treated triticale between their vineyards in winter.
The mycorrhiza moved over to the vines in the summer via the larger mycelium network,” Dr Venter noticed. F or mycorrhiza to work effectively it must also be managed and treated properly, and planted as close to the roots as possible. It’s also sensitive to certain pesticides and fertilisers, but Dr Venter points out there are suitable alternatives for almost every unsuitable product. For example, farmers will still be able to use fungicides such as Raxil and Ingwe to treat wheat seed.
Baobab, a new fruit for the worlds
Consumers in industrial countries are constantly looking for new foods and exotic fruit can exploit this market. A frica’s substantial biodiversity includes many indigenous fruit trees and shrubs traditionally used for food, drinks or health. Rooibos has already made its international mark, and is being followed by honeybush, devil’s claw, hoodia and buchu for their health benefits. Baobab seems set to join this trend. In SA, baobab is seen as a unique oddity and its shape has led to the nickname of upside-down tree.
There are nine known baobab species, seven of which occur in Madagascar, where one can also find a baobab nature reserve. Many of these species are bottle-shaped. The flowers are pollinated by fruit bats and the fruits are packed with nutrients that include vitamins A, C, D, and E, as well as riboflavin, niacin, pectin, and citric, malic and succinic acids. It is also a probiotic that can stimulate intestinal flora. fter rigorous assessments for safety and benefits, the UK Food Standards Agency has just granted PhytoTrade Africa, a Southern African regional association for natural products, and Afriplex approval to market baobab pulp as an ingredient in various processed foods. Sustainable harvesting still needs to be considered. – Wynand van der Walt ([email protected]) Sources: FoodNavigator July 2008. |fw