RE: Mycorrhizae research and web source

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Dr. Vicki Bess, at BBC Labs in Temple, AZ is a leading expert on compost and compost tea.  She is a key note speaker at the upcoming international composting symposium at Ohio State Univ in April.  There is a ton of very useful information at http://www.bbclabs.com/toppage3.htm

Here is just one article on the mycorrihizae topic of discussion. Send mail to i*@bbclabs.com with questions or comments. 

Susan McCoy

VA Mycorrhizae (VAM) in Agriculture

 What Are VA Mycorrhizal (VAM) Fungi?

VA mycorrhizae [alias: vesicular arbuscular mycorrhizal fungi (VAM) and arbuscular mycorrhizal fungi (AMF)] are beneficial fungi that penetrate and colonize the root of the plant, then send out filaments (hyphae) into the surrounding soil. The term mycorrhizae literally means "fungus-roots" and VAM is considered endomycorrhizal since it colonizes the interior of the root.

How Do VAM Fungi Work?

VAM fungi are associated with the plant in a mutually beneficial relationship. The VAM fungi, nestled inside the root, sends out long filaments or hyphae to explore up to 200 times the soil area available to the root alone. The hyphae literally form a bridge that connects the plant root with large areas of soil and serves as a pipeline to funnel nutrients back to the plant. In return, the plant must supply the VAM fungi with carbon for the fungal growth and energy needs.

This plant-fungal relationship is an elegant association and its development is evidently regulated by several factors. The promotion of root colonization by the VAM fungi is enhanced by different soil bacteria known as "mycorrhizal helper bacteria". The presence of these bacteria, many of which are aerobic heterotrophic bacteria such as Bacillus sp., probably affect VAM colonization and function by their production of vitamins, hormones, and other compounds. Plants produce discharges (exudates) sent out through their roots that contain specific compounds acting to stimulate the VAM hyphae growth.

Why Do Your Plants Need VAM Fungi?

Fortunately, most crops can be colonized by VAM fungi. The VAM fungi are best known for their ability to improve plant growth in low phosphate soils by exploiting large areas of soil and actively transporting the phosphate back to the plant. Other benefits to the plant supplied by the VAM colonization include increased absorption of nitrogen, potassium, magnesium, copper, zinc, sulfur, boron, molybdenum and other elements that are transported back to the plant. Due in part to the association of particular bacteria with the VAM fungi, many of these non-mobile elements are made water soluble by bacteria, absorbed by the VAM fungi, and translocated to the plant through the VAM "pipeline".

VAM fungi can increase the disease resistance of plants against root pathogens, especially when the VAM fungi can adequately colonize the root before the pathogen attacks. VAM fungi are important in forming stable soil aggregates by binding soil particles in the filamentous mass as well as producing sticky substances that hold the particles together. Due mainly to improved plant nutrition, VAM colonization can also improve plant drought resistance.

Agricultural Practices That Are Harmful to VAM Fungi.

VAM fungi can be severely impacted by the application of some fungicides and fumigants. Soil disturbances such as discing may destroy the hyphae network connections to the plant roots. VAM fungi are also reduced by extensive fallowing and floods.

What Tests Measure VAM Fungi?

The concentration of VAM fungal spores in the soil can be measured and used as an indicator of potential for VAM colonization. For most situations, it is better to actually test the plant roots for the percentage of VAM colonization as a true indicator of the extent of VAM activity.

 Copyright © 1999 Vicki H. Bess, BBC Laboratories, Inc.