How Mycorrhizal Fungi Benefit Plants

Better uptake of nutrients
With the help of mycorrhizal fungi, a plant can take up many times more nutrients, particularly phosphorous, than would be possible in the absence of the fungi. When a dependent plant lacks mycorrhizae, growers often have to load the soil with high levels of soluble nutrients. This heavy feeding is expensive, and further damages the health of the soil and water.

Soil improvement
Mycorrhizae enhance the soil by improving the structure of soil. This helps to increase water holding capacity, and traps nutrients that otherwise could be leached by rains.

Faster rehabilitation of degraded sites
Because they enhance the plant's ability to take up nutrients and water, mycorrhizal fungi can help plants compensate for low nutrient availability, poor soil structure, low water holding capacity often prevalent on harsh sites.

Healthier plants, less disease and fewer pests
Most experts in integrated pest management say that plant health is the most important aspect of pest management--healthy plants have much fewer pest problems. Better nutrition and water uptake through mycorrhizae helps plants stay healthy.

Biocontrol of certain pathogenic organisms
By infecting the root system of a plant, mycorrhizae can interfere with pathogenic organisms, effectively protecting the host plant from diseases.

Tolerance for problem soils
Mycorrhizal fungi may also help regulate the uptake of soil toxins, allowing plants to better tolerate salty or problem soil conditions.

Mechanism of disease suppression by mycorrhizal fungi

Parasitisim of pathogen by mycorrhizal fungi
Ø Mycorrhizal chlamydospores have been reported to occupy seeds and dead insects in soil and have limited saprophytic capabilities. It seems likely that mycorrhizal fungi colonize only stressed or weakened nematode eggs.
Ø The nematode parasitism by mycorrhizal fungi is opportunistic and depends on the carbon nutrition from autotrophic symbionts, rather than being representative of a true host-parasite relationship.

Change in root morphology
Ø Root offers structural supports to plants, functions in of water and mineral nutrients, are the site of production of growth regulators, are a sits of starch storage and provide a nutrient supply for a wide range of microorganisms.
Ø Change in root morphology ultimately affects their responses to other organisms.
Ø Mycorrhizal plants also have a strong vesicular system which imparts greater mechanical strength to diminish the effects of pathogens.

Histopathological changes
Ø Mycorrhizal fungi had fewer giant cells and smaller syncytia which confer resistance against the nematode in the host plants.
Ø Nematodes developed in mycorrhizal plants were smaller in size and took longer time to develop into adults.

Physiological and Biochemical changes
Ø The physiological changes caused by mycorrhizal fungi in the host plant generally reduced the severity diseases.
Ø Phenolic compounds formed after mycorrhizal colonization has been thought to play important role in the defense resistance.
Ø Inoculation of mycorrhizal fungi also increased the level of phytoalexin in plants, which play a major role in the host defense system against the pathogens.
Ø Inoculation of mycorrhizal fungi increased the level of amino acids (phenyalanine and serine) in the host plant and it is assumed that these amino acids having inhibitory effect against the root pathogens.

Change in host nutrition
Ø Improved the phosphorus nutrition.
Ø Mycorrhizal fungi induced decreased in root exudation, which has beeen the cause of reduction of soil borne diseases.
Ø Mycorrhizal fungi can also affect changes induced by environmental stress in root growth, root exudation, nutrient absorption and host physiology.
Ø Mycorrhizal fungi in P-deficient plant affected membrane permeability and exudation pattern in a way similar to that caused by P-fertilization in non-mycorrhizal plants.