Mycorrhizae Part II

Mycorrhizae Part II

  • By Cleve Campbell
  • /
  • December 2015-Vol.1 No.12
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After reviewing last month’s Garden Shed article on mycorrhizal fungi, I sat down at the PC and started doing a little Christmas shopping for my bride; what a more fitting gift than a couple of pounds of fungi to add to the garden. After gleaning a little general information from last month’s article on the benefits of  mycorrhizal fungi to plants including how the fungi:

  • extends the plants root system allowing the plant to absorb nutrients better, particularly phosphorus,
  • increases the plants ability to absorb water, making the plants more drought resistant,
  • increases the life of root hairs by protecting the roots from diseases,
  • improves the physical condition of the soil

I know it will be the perfect and unexpected gift-“the gift that keeps on giving”. If you somehow missed reading last month’s article, Mycorrhizae Part 1 or  if you wish to review the introduction to this friendly alley, go back to the 2015 November Garden Shed issue.

I’m sure this will be the perfect gift and a little PC search revealed there must be a zillion fungi products on the market claiming to be the silver bullet, the fix all, from increasing crop production to equipping the plants with a Kevlar vest to protect your plants from an army of pathogens. Yes, I know it’s the holiday season, the giving season, but being somewhat of a frugal gardener, I needed to do a little more research before I pull the trigger and throw a few bucks on a frugal purchase.

My first step is to determine what “variety” of mycorrhizal would benefit the vegetable garden. There are two types of mycorrhizal fungi that I had to choose from: ectomycorrhiza and endomycorrhiza. The ectomycorrhiza group includes hundreds of fungal species associated with shrubs and trees, such as pine, birch, hemlock and oak. These fungi, cover the surface roots with a mantle. I can exclude the ectomycorrhiza as a choice for the vegetable garden.  (now if I was planting trees that would be a different story). (Brady)

The next type endomycorrhiza with the most important member or this group being  arbuscular mycorrhiza fungi (AMF). When forming AMF, fungal hyphae (microscopic thin strings) actually penetrate the cortical root cell walls and once inside the plant cell, form small highly branched structures called arbuscules. These structures serve to transfer mineral nutrients from the fungi to host plants and sugars from the plant to the fungus. Most native and agriculture crops can form beneficial relations with AMF. I now have my fungi variety selected for the vegetable garden. (Brady)

My second step is to determine if my vegetable garden would benefit from an arbuscular mycorrhizal fungi (AMF) inoculant treatments. Numerous studies at Penn State have shown that arbuscular mycorrhizal fungi (AMF) can provide direct benefits to host crops, leading to increased crop production. As it turns out AMF can have a positive effect on most crops with the exception of spinach and brassicas such as broccoli and cabbage. A research project conducted by the University of California concluded that organic tomato plants infected with AMF out performed non-infected plants. A potato research project at Texas A&M found that potatoes treated with AMF increased phosphorus, iron and magnesium uptake, greater water uptake, as well as enhanced disease resistance, resulting in greater crop yields.

One of the issues for determining the need for AMF in any situation is they are microscopic and they occur in nearly all-natural and agricultural soils and readily colonize on many plant species. Herein lies a problem. The research articles reviewed often used potted plants with a sterile soil mixture or in  field sites where the native AMF populations were very low. Sites were  selected where soils were subjected to broad-spectrum fumigation or the soils that had been drastically disturbed such as subsoil layers being brought to the surface during construction activity and soils that had been left bare (fallow) for long periods of time. In those types of situations plants inoculated with AMF out performed the plants that were not inoculated. (Brady)

In healthy biologically active soils little difference was noted between AMF inoculated plants and non-inoculated plants. One possible reason proposed that in soils with sufficient phosphorus levels, the plant was able to supply their needs without the symbiotic relations of the fungi and thus did not form a relationship. (Brady)

Well, as it turns out, soils in a natural setting are full of beneficial soil organisms including mycorrhizal fungi. Soils that are high in organic matter, well drained, low to moderate phosphorous levels and minimally tilled, usually have a healthy and abundant  network of mycorrhizal fungi. (Plaster)

Fungicide applications can kill mycorrhizal fungi. In addition, frequent tilling breaks apart the fungal networks reducing their effectiveness and high phosphorus levels render the fungi useless.  All of a sudden that vision of last spring’s finely tilled seed bed was not such a fond memory, not to mention the numerous trips to the garden in the late spring and summer to chop and till all those weeds, and the late fall tilling to put the garden to bed, OUCH! (Plaster)

Areas with untasseled corn were fallow areas Photo courtesy of Penn State Extension

Areas with untasseled corn were fallow areas
Photo courtesy of Penn State Extension

Did I mention that I never got around to planting a cover crop last fall? That didn’t help the mycorrhizal population in my garden either, as uncovered soil (fallow) can reduce mycorrhizal populations. Remember, mycorrhizal fungi depend on host plants for their nutrition, thus planting a cover crop can help to maintain their population. (Brady)

One method of determining if my soil has an adequate population of mycorrhizal fungi is by performing a soil test. However, it requires a biological test not a chemical test, that measures pH levels, phosphate, potassium, magnesium levels and other chemical properties. An online search on “soil biology tests” revealed numerous commercial labs that perform the test. The price ranges from $100-$400 bucks depending on the lab and the number of biological critters you wish to be identified. The second option is to do a practical test next spring, such as treating potatoe, tomato, pepper and lettuce crop with mycorrhizal fungi and monitor the difference between the inoculated and the non-inoculated crops. If the inoculated plants are more productive than untreated plants, then it becomes obvious. I have a mycorrhizal fungi deficiency in my garden.

I recall seeing inoculants listed in various mail order seed catalogs and online seed catalogs, so I am just a click away from the perfect gift. Could this be any easier? A trip to one of my favorite online catalogs and a quick search on inoculant and I was done. I was able to locate the inoculant products on the first click. My quick search resulted in several choices: one for peas, lentil and vetch, a second choice for soybeans, and third choice “ a combination” for peas beans, vetch and more. That is when the red flag went up. I had just read a publication that AMF can have a “positive effect on most crops”. The seed catalog said nothing about tomatoes, corn, and peppers or referred to any other crop other than legume crops. Hummm, what’s the deal?

After doing a little research, it turns out that legume inoculants and AMF are totally different, legume inoculants are a form of bacteria and AMF, well they are a form of fungi and play an entirely different roll when they form symbiotic relationships with plants. (Plaster)

Legumes have the ability to form mutually beneficial relations with certain soil bacteria of the type or genius Rhizoba. The benefit to the plant is that these bacteria can take (fix) nitrogen from the air found in soil air spaces and make it available to the plant via symbiotic nitrogen fixation. The amount of nitrogen fixed can meet the needs of the plant and leave nitrogen in the soil for the following crops. Mycorrhizal fungi (AMF) aid the plant by foraging for water and nutrients in the soil.

Why the legume inoculants choices in the seed catalog?  Well, it appears that Rhizoba bacteria are picky little critters and are fairly specific about which legume species they will select as a host to form nodules. So if you are selecting legume inoculants it’s important to select the correct type for your legume. (Plaster)

Now that I have determined that  legume inoculants and AFM inoculants are two different critters, a quick online search for mycorrhizal (AFM) products resulted in locating numerous products on the market. Digging a little deeper I discovered that Cornell University has performed numerous research studies on a mycorrhizal strain, Trichoderma barzianum strain T-22 sold under the trade name of T-22.

The studies at Cornell University concluded that this strain (T-22) of mycorrhizal fungi increased plant growth and yield by increasing nutrient uptake and fertilizer efficiency. The plants increased drought tolerance was attributed to increased root growth in the treated plants. In addition, according to Cornell, T-22 was shown to act as a biocontrol for certain plant diseases: tomato transplants treated with T-22 at the start of the growing season were substantially less susceptible to early blight than the untreated plants.

Now back to my AMF experiment, I must be vigilant in designing my AMF experiment by selecting  the same vegetable cultivars for my test, because final results may vary as not all vegetable cultivars respond to AMF inoculation in a consistent matter.  Research performed on green house lettuce suggested that a green cultivar (Batavia Rubia Munguia) reacted in a more positive way to AMF inoculants than did a red lettuce cultivar (Maravilla de Verano). Similar research on the effect of AMF inoculants on tomatoes suggested that different cultivars of tomatoes performed differently when treated with AMF inoculants.

What’s not to like about mycorrhizal fungi? They perform like an organic biofertilizer, they forage for water, phosphorus and other nutrients that plants cannot reach, resulting in healthier and more productive plants and they are organic. Next spring, when I roll out the tiller or bag of commercial fertilizer I’m going to think about my fungi friend in the ground and do a lot less tilling and a lot less fertilizing because you just don’t do harmful things to a good and valuable friend.

Thanks for stopping by The Garden Shed, and we The Garden Shed team hope you and your family have a safe and joyful holiday season. By the way if you have run out of gift ideas, why not consider a bag of mycorrhizal fungi because it is the natural gift that keeps on giving, Happy Holidays!


Penn State Extension, “Mycorrhizal Fungi and Field Crops”                       

The University of Georgia Extension, “Soil Inoculants”, Publication C990

The Nature and Properties of Soils (Brady,N., 2008), pp. 471-475.

Soil Science and Management (Plaster,E.,2009), pp. 109-117.

University of California, ” Arbuscular Mycorrhizas, Microbial Communities, Nutrient Availability, and Soil Aggregates in Organic Tomato Production”

Texas A&M, “Influence of a Flavonoid (Formononetin) on mycorrhizal activity and potato crop productivity in the highlands of Peru” http://aggie-horticuhttp://Texas A&M Mycorrhizal fungi effect on potatoes

Cornell University, TRICHODERMA SPP. FOR BIOCONTROL                       

eXtension, “Legume Inoculation for Organic Farming Systems “             

Journal of Agricultural and Food Chemistry, 2011, 59 (20), pp. 11129-11140, “Improvement of Nutritional Quality of Greenhouse-Grown Lettuce by Arbuscular Mycorrhizal Fungi is Conditioned by the Source of Phosphorus Nutrition”.

Annals of Botany, 1998, 82:849-857, Article No bo980768, “Mycorrhizal Response of Two Tomato Genotypes Relates to their Ability to Acquire and Utilize Phosphorus”.

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