Mass Production Techniques of Arbuscular Mycorrhizal Fungi
Authors: Ajit Kumar Dubedi Anal, Manwendra Singh and Mritunjay Tripathi

Arbuscular mycorrhizal (AM) fungi are ubiquitous in distribution and occur over a wide range of agro-climatic conditions. AM fungi form symbiotic associations with the roots of almost 80% of the land plants (Akhtar and Panwar 2011; Smith and Read, 2008). AM fungi are characterized by the presence of their unique extra radical mycelium branched haustoria like structure within the cortical cells, known as arbuscules. (Smith and Read, 2008). The role of arbuscles is to increase the surface area of roots during nutrient transfer. AM fungi colonize the plant roots and penetrate into surrounding soil, extending the root depletion zone and the root system. AM fungi have improved the growth of host plant due to increased nutrient uptake, production of growth promoting substances, increase tolerance to drought, salinity and synergistic interactions with other rhizospheric microbes.

There are three major well know systems for the mass production of AM fungi. These are substrate based production system, substrate free production system and in vitro production system.

1. Substrate based production system:

In this method first the plants and their associated symbionts were cultivated in soil or sand based substrate. After the initial production of AM fungal inoculums, these fungi were propagated for the mass multiplications by using a single species or a consortium of identified AM fungal species in clay or plastic pots or scaled up to medium-size bags and containers and large raised or grounded beds The starter inoculums usually consist of a single or a consortium of spores and infected root segments. In order to prepare the after inoculums, the root segments are dried and chopped into fine pieces to obtain the mixed inoculums, while, wet sieving and decanting techniques were used to obtain the single spores. Mixed inoculums were commonly used for the production of those AM fungal species which may produce intra-radical spores and vesicles (Klironomos and Hart, 2002).

Advantages:-

• This system preserved the mass production of single or consortia of AM fungal species.
• Regular and properly monitoring of the nutrient supplies to the AM fungus and plant could require.

Disadvantages:

• Requirement of controlled culture conditions, and also be a chance for superfluous contaminants.

2. Substrate free production system:-

In this type of system, where the nutrient solution is aerated through an aeration pump to avoid the roots suffering from oxygen deprivation. The pumps must be switched on periodically to minimize the flow of nutrient solutions and stuffed of air bubbles, which might be damage the expansion of the delicate extra radical hyphae.

A. The nutrient flow technique

It has been initially introduced by Mosse and Thompson (1981). The nutrient flow technique is an alternative system in which a thin nutrient solution covers the roots and increases the relative area for gas exchange.

B. Aeroponics:

Aeroponics is a kind of hydroponics systems involves the dipping of roots of host plant and AM fungal propagules in nutrient solution .Spraying of micro-droplets increases the aeration of the medium, and the liquid film surrounding the roots imparts gas exchange.

Advantages :

• The main advantage of this system is the production of substrate free inoculum.

Disadvantages:

• The liquid nutrient solutions are highly prone to the growth and development of algal contaminants.

• The spore production rates could also be affected by lack of a carrier substrate.

3. In-vitro production system

In-vitro production system of AM fungi was first established by Mosse and Hepper (1975).

Mass scale production of AM fungi was achieved by root organ culture in small containers. In an airlift bioreactor and in a mist bioreactor with perlite as a substrate or in a bioreactor containing solid. Several investigators in the past have used many complicated in-vitro systems for the propagation of AM fungi has developed a system in which the shoot was always outside of Petri plate while, the roots and AM fungus was associated inside the Petri plates filled with a suitable gelled medium. However, in the de Boulois et al. (2006) system the shoot was developed in a sterile tube vertically connected to top of a Petri plates, which the root and AM fungus was in close association inside the Petri plates. Moreover, the in-vitro system developed by Declerck et al. (2009) the preinoculated plants produced individually introduced AM fungal inoculum in a sterile growth tube in a closed system running with nutrient solution.

Advantages:-

• The lack of unwanted microorganisms makes this system more appropriate for the mass production of high quality of AM fungal inoculums.

• There is always requirement for monitoring and regulating the cultures.

• To make this system cost effective skilled technicians and laboratory equipments were also required.

Disadvantages:

• In-vitro plant cultures need regular additions of culture medium which might be increase the risks of cross contamination.



About Author / Additional Info:
I am working as a Young Professional-II in ICAR-NRC on Litchi.