Re: Does root growth enhancer help bean seeds to grow faster?

Plants have formed a variety of partnerships with fungi, bacteria and animals. 
The most common plant-fungus partnership is between a mycorrhizal fungus and a 
root, which together form a mycorrhiza or "fungus-root." The fungus benefits 
the plant by increasing mineral nutrient absorption, particularly phosphorus, 
and possibly water uptake. The thread-like hypha of the fungus explore the soil 
more efficiently than normal roots. The root provides food and a home for the 
fungus.

There are several types of mycorrhiza. The ectomycorrhiza are very different 
structurally than a normal root, and the fungus are not within the root cells. 
In endomycorrhiza, the fungus is within the plant cells so the root must be 
examined under a microscope to see the fungus inside.

Phosphorus is often present in soils but unavailable for plant uptake because 
it is in an insoluble form. Thus, plant scientists measure plant available 
phosphorus. High levels of available phosphorus will inhibit the development of 
mycorrhiza. Thus, it may be difficult to establish mycorrhiza in potted plants 
if the growing medium contains appreciable soluble phosphorus or a regular 
fertilizer, which has high soluble phosphorus, is used. If you use no 
fertilizer, the plants may grow poorly due to lack of all mineral nutrients. It 
might be desirable to irrigate with a fertilizer lacking phosphorus to see if 
the mycorrhiza make up for a low available phosphorus level in the soil. 

What brand of endomycorrhizal root growth enhancer are you using? Root 
inoculation with mycorrhizal fungus has not been completely perfected although 
large crop increases can occur on  soils with low phosphorus availablity. One 
complication is that endomycorrhiza are obligate symbionts so cannot be 
produced without a plant. Another complication is that a single plant may 
normally host several species of mycorrhizal fungi.  

Is there a reason for choosing a mycorrhizal enhancer? It can be rather tricky 
experimentally to do mycorrhizal experiments with soilless potting soil because 
they usually have low total phosphorus once the initial charge of soluble 
phosphorus is gone. Soilless potting media are designed to be fertilized 
frequently, either weakly or with every irrigation.

With bean you could more easily get a clear response if you innoculated half 
the plants with nitrogen-fixing Rhizobium bacteria. The nitrogen-fixing root 
nodules are easy to see without a microscope.  

References


An Above Grounder's Introduction to Mycorrhiza


Kinds of Mycorrhiza


Introduction to Mycorrhizas


Study on utilization of arbuscular mycorrhizal fungi in kidney bean 
cultivation - Effects of available phosphorus content on the infection of 
arbuscular mycorrhizal fungi and two species of arbuscular mycorrhizal fungi on 
the growth of kidney bean (Phaseolus vulgaris L.)