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  • From: "Lon J. Rombough" <lonrom@hevanet.com>
  • To: NAFEX <nafex@lists.ibiblio.org>
  • Subject: [NAFEX] Fwd: Mycorrhizae
  • Date: Fri, 9 Apr 2010 10:29:33 -0700

From another list.


We have had discussions about mycorrhizal fungi on this list before.  There is some disagreement about the utility of inoculating vines with products that contain one or more types of these fungi.

He is a brief synopsis, from MY understanding and opinions.

Mycorrhizal fungi, most of which are arbuscular mycorrihizal fungi (AMF) or vesicular-arbuscular endomycorrhizal (VAM) fungi, form a symbiotic association with the roots of many plants.  In a symbiotic relationship, each organism gets something of utility from the the other organism.  The fungi get carbon nutrition from the host plant (vines) and the fungi increase the ability of the host plant roots to extract phosphorus from the soil, especially when the level of P in the soil is low.  Plants with higher AMF populations also have been shown to increase absorption of a number of micronutrients and survive drought better, but this may just be a secondary effect from the greater growth of the plants due to P availability.

A few types of plants are basically obligate symbionts, and require AMF to grow.  Grapes are not obligate to AMF, but it has been known since the early 1970's (Possingham and Grrot Obbink 1971), that  grapes can benefit nutritionally from an AMF symbiosis.  Almost all wild and cultivated vines that have been examined have some level of AMF colonization on their roots.  However, the AMF population varies greatly, seasonally and annually, on the same vine; but generally increases during the growing season.

Since the majority of plant species have an AMF symbiosis, the fungi are present in almost all native soils.  AMF populations are low in sterilized soils and soils that have been kept plant-free for a long time (AMF are obligate symbionts).  There are a number of species of AMF.  The distribution a a particular AMF species is more dependent on soil conditions, rather than the distribution of a particular host species; because most AMF species colonize a very large range of plant species.  So,  except in sterilized soils, there is generally a good population of AMF species in natural soils that are well adapted to those soil conditions.  If you plant a host plant (vine) in a natural soil, the roots are fairly rapidly colonized by the native AMF species to the population level that is possible under the soil and environmental conditions.

So, the issue is not, do vines benefit from AMF? (they do), but does using a commercial inoculant of AMF confer any advantage to the vine over the natural colonization of AMF that will occur when a vine is planted in natural soil.  Clearly in sterilized soils and highly disturbed soils, there is a good argument that natural AMF populations are low, and supplemental inoculation will benefit a vine.  It has also been shown that AMF populations on vines are higher in soils with low available P levels, where the symbiosis provides the greatest benefit to the vine.  Again, if you have a soil that is low in P, an argument can be made for AMF inoculation.  Most recent studies have show that absent those conditions, inoculation with AMF has little to no benefit over natural AMF colonization from the soil.  Also, when AMF populations on inoculated vines are examined a year after planting, the populations on the vine roots are the types of AMF species that are found in natural soil, and not the types that were in the inoculant.

One of the researchers has has done the most work on AMF and grapevines is in your neck of the woods, Paul Schriener works at the USDA ARS lab in Corvallis.  You can Google him or contact him.  Remember, when looking at research, note whether the vines were growing in sterilized soil or in a poor-P condition.

I posted a link a couple years ago to a researcher that looked at the viability of commercial AMF inoculant products and found over half of them had extremely low levels of viable spores, and thus are mostly a waste of money regardless of whether AMF inoculation provides a benefit.  Since that research is now out-of-date, the site is no longer maintained, but I doubt the situation has changed much.

I know it sounds crazy, but try to get your information about these issues from sources that are not trying to sell you something or benefitting from their advertising. 

And to end, there are some potting media formulations that provide AMF spores as part of the media mix at essentially the same price as mixes without AMF.  Since soil-less media are mostly sterile, this can be of benefit.  Premier Horticulture's Pro-Mix BX with Mycorise Pro is one I have used with good results:
http://www.premierhort.com/eProMix/Horticulture/Products/GrowingMediumTM/ProMixBX/BXRegular/fProMixBX.htm
http://www.premierhort.com/eProMix/Horticulture/Products/GrowingMediaCat/mycorise/fBiostimulant.htm




On Apr 8, 2010, at 10:49 PM, wrote:

<x-tad-bigger>Glen and Leroy Creasy refer to research done on Mycorrhizae in their book "Grapes."  They say the form of Mycorrhizae, VAM, acronym for vesicular-arbuscular mycorrhizae, are the most common form associated with grapes especially in low phosphorus soils.  References are:  Possingham and Groot Obbink, 1971;  Deal et al. 1972;  Biricolti et al 1997;  Aguin et al 2004; so maybe it isn't all salesmanship.   </x-tad-bigger>


  • [NAFEX] Fwd: Mycorrhizae, Lon J. Rombough, 04/09/2010

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