Introduction
Grapevines have a coarse and poorly branched root system that produces relatively large diameter fine roots. Because of this, grapevines appear to be more reliant on Mycorrhiza (Endomycorrhizae) fungi colonisation for normal growth and development than fine-rooted species (Mohr, 1996, Van Rooyen et.al. 2004). These vines seem to be highly dependent on Mycorrhiza (AMF) to obtain sufficient nutrients and water for normal growth, even under salty conditions (Al-Karaki, 2000)The “Extra root system”AMF supplies the plant with an “extra very efficient root system” consisting of microscopic fibres called hyphae. These hyphae grow and form a vast mycelium network in the soil increasing the absorption surface for nutrients and water by 300%. (Fig.1)

According to Smith & Read (2009), hyphae of AMF extend into the soil far beyond the root surface or root-hair zone (up to 25 cm has been measured) The mycelium network (extra root system) reaches places where normal roots would not fit. Pockets of nutrients and water in the soil which were once unreachable by the root system, are now made accessible through the “mining” effects which AMF hyphae gives to the plants (Smith & Read 2009). Their smaller diameter means that marked depletion zones do not develop around them and, furthermore, they are able to grow into soil pores that roots with much larger diameters are unable to access. (Fig.2)

The functions of the “Extra Mycorrhizal root system”

1. Better establishment

A strong dependency on AMF during the establishment of grapevines was shown by Menge et. al (1983). It was found by Agiun Olga et.al (2004), that grapevines inoculated with AMF resulted in a finer more branched root system. Fewer fatalities occurred and even growth of the vines was observed during the first year (Fig.3)

2. Mineral and water uptake

AMF are best known for their contribution to mineral uptake by plants, particularly those minerals that have limited mobility in the soil, such as phosphorus (P), zinc (Zn) and copper (Cu) (Marschner 1995). Through its extra root system of mycelia, AMF especially seeks out P and the acidic exudates of AMF, solubilise fixed P, absorb the P and translocate it to the plant root. Another example is potassium (K) whereby AMF reduces K leaching and helps it gain access to K trapped between clay platelets in some soils. Fertiliser prices are escalating and there is no end in sight as the non-renewable resources are running out. One strategy is to reduce reliance on these inputs, as well as increase their efficiency. AMF can be a key to this as it effectively enables recovery of past fertiliser investments (Sait, 2012).

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Wynboer – March 2013 – Why is Mycorrhiza important for grapevines

Wynboer - March 2013 - Why is Mycorrhiza important for grapevines Wynboer - March 2013 - Why is Mycorrhiza important for grapevines

 

3. Alleviates stress

Furthermore the “extra root system” of AMF alleviates environmental stresses such as transplant shock, drought, hail, nutrient deficiency, water logging etc. For instance, some drought-sensitive rootstocks (775P,101-14Mgt and 5BB) colonised with AMF and subjected to drought for eight days showed much improved drought resistance compared to non-AMF rootstocks of the same varieties (Van Rooyen et. al 2004 Nikolaou, Angelopoulos & Karagiannidis 2002, Smith & Read 2009).

4. Boosts a plant’s immune system and suppresses diseases

This beneficial fungi forms antibiotics, thus causing the plant to be more tolerant to diseases i.e. Phytophthera, Fusarium, Pythium, Phyloxera, Nematodes etc. (Pfleger and Linderman 1994). It also boosts a plant’s immune system. Another example of the effect that AMF can have on a plants immune system was found by Gange et. al (1994), where AMF vines providedsome degree of resistance in roots against black vine weevil larvae at low larval densities.

5. Builds soil structure

Glomalin (a “glue”) is a glycoprotein produced in large amounts by AMF, that in turn binds soil particles together. Greater aggregate stability of soils improves infiltration of water, gas exchange and resistance to erosion (Schreiner, 2005, Smith & Read 2009), as well as increasing the cation exchange capacity of the soil. It has also been suggested that AMF is involved in carbon sequestration, which can be important for carbon credits (Smith & Read 2009, Sait, 2012) The result of the above mentioned benefits, is a larger root system, thicker stems and a healthier grapevine that yields more fruit with a higher quality i.e. brix. AMF in return receives carbohydrates from the plant. (Schreiner 2004, Smith & Read 2009) This symbiotic relationship is prevalent in nature.

Influence of cover crops

Cover crops are often planted between vine rows to reduce soil erosion and improve soil fertility and structure. Assuming grapevines and cover crops share AMF species contact among grapevines and cover crop roots may lead to development of a common AMF-network that, in turn, may facilitate direct nutrient transfer from cover crops to grapevines. Overlap of AMF between these two crops may enhance below-ground interactions (Cheng & Baumgartner, 2004).

Humic and fulvic acids are bio-stimulants derived from decayed organic matter i.e. compost, lignite, leonardite. Humic acid differs in the soil, in that it is 10 times larger, more stable in the soil and it is less compatible with fertilisers than fulvic acids. These humates help break up clay and compacted soils. They provide sites for micro-organisms to colonise. They assist in transferring nutrients from the soil to the plant, enhance water retention and stimulate development of micro-organisms.

The bacteria secrete enzymes which act as catalysts, liberating calcium and phosphorous from insoluble calcium phosphate, as well as iron and phosphorous from insoluble iron phosphate This phosphate can promote root – and AMF growth. (Sait, 2012 Anon, 2001). Compost is a “biological inoculum” and improved soil structure, aeration, porosity and crumb structure are all linked to it. These beneficial0 micro-organisms restore biodiversity and the balance that comes with it. This balance creates a disease suppressive soil. Compost increases the CEC, which is particularly important in light soils. It contains humus with its benefits as discussed above. Even earth worms are evident when compost is applied (Sait 2012)

Conclusions

The “extra root system” of AMF enables these beneficial fungi to utilise nutrients and water more efficiently from i.e. organic compounds than the coarse roots of the grapevine thus benefiting the producer in the long-term.

References

Al-Karari, 2000. Growth of mycorrhizal tomato and mineral acquisition under salt stress. Mycoorhiza 10:51-54.
Agiun, O., Mansilla, J.P., Vilarino, A & Sainz, M. J., 2004. Effects of mycorrhizal inoculation on root morphology and nursery production of three grapevine rootstocks. Am.J. Enol. Vitic. 55:1:108-111.
Anon., 2012. Humic acid structure and properties. www.phelpstek.com/ fertfoliar/samples/humic-acid.html.
Cheng, X & Baumgartner, K., 2004. Overlap of grapevine and covercrop roots enhances interactions among grapevines, cover-crops, and arbuscular mycorrhizal fungi. Proceedings of the soil environment and vine mineral nutrition. San Diego, CA., June 29-July 2. 2004.
Gange, A.C., Brown, V.K & Sinclair, G.S., 1994. Reduction of black vine weevil larval growth by vesicular-arbuscular mycorrhizal infection. Entomologia Experimentalis et Applicata. 70:2:115-119
Cheng, L., Fitzgerald, L. B., Cong T.,Burkey, K.O., Shew, H. D., Rufty,
T.W & Shuijin, H., 2012. Arbuscular mycorrhizal fungi increase organic carbon decomposition under elevated CO2. Science 337, 1084.
Marschner, H., 1995. Mineral nutrition of higher plants. 2d ed. London
Academic Press. San Diego, CA. 570.
Menge, J.A., Raski, D.J., Lider, L.A., Johnson, E.L.V., Jones, N.O., Kissler,
J.J. & Hemstreet, C.L.,1983. Interactions between mycorrhizal fungi, soil fumigation and growth of grapes in California. Am.J.Enol.Vitic. 34,117-121.
Mohr, 1996. Periodicity of root tip growth of vines in the Mosselle valley.
Vitic.Enol.Sci.51:83-90.
Nikolaou, N., Angelopoulos, K & Karagiannidis, N., 2003. Effects of drought stress on mycorrhizal and non-mycorrhizal Cabernet Sauvignon grapevine, grafted onto various rootstocks. Experimental Agriculture. 39,3,241-252.
Pfleger, F.L & Linderman, R.G.,1994. Mycorrhizae and plant health.
Symposium series. Am. Phytopathol. Soc. Minnnesota.
Sait, G., August 2012. Banking on biology-managing your minerals.
Sustainable agriculture seminar. Stellenbosch.
Schreiner, R.P., 2005. Mycorrhizas and mineral acquisition in grapevine.
Soil Environment and vine mineral nutrition. 49-60.
Smith, Sally E & Read, D .,1997. Mycorrhizal symbiosis. Academic Press.
San Diego. CA.
Van Rooyen, M., Valentine, A & Archer, E., 2004. Arbuscular mycorrhizal colonisation modifies the water relations of young transplanted grapevines
(Vitis). S.Afr. J.Enol. Vitic. 25:2:37-41

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