Mycorrhizal association for strengthening root system of tissue culture derived plants
Author: Dr. Vartika Srivastava

Tissue culture technology and its importance:
Tissue culture technology is most widely accepted method of large scale multiplication and regeneration of quality planting material throughout the world. In vitro propagation provides excellent advantages over traditional propagation by way of high multiplication rate, physiological uniformity, year round availability of disease-free material, rapid dissemination of new plant materials throughout the world, uniformity of shoots, short harvest interval and faster growth in the early growing stages compared to conventional materials. Tissue culture also plays a vital role in the distribution and conservation of germplasm, safe exchange of planting materials and rapid propagation of newly selected hybrid cultivars.

Hardening and plantlet survival:
In certain plant species, establishment of tissue culture raised plants under glasshouse and later in field is often very poor. This is mainly attributed to the inability of such plants to tolerate different type of stresses such as transplant shock, excessive water loss, pathogen attack, poor photosynthesis, poorly developed root systems etc. The survival percentage across the genera depends upon the root development and its nutrient uptake ability during hardening phase. During transport and field establishment plantlets are frequently exposed to adverse environmental conditions that have a negative effect on plant survival, development and productivity. Drought is considered the most important abiotic factor limiting plant growth and yield.

Benefits of mycorrhizae:
Mycorrhizal inoculation to in vitro propagated transplants has been found effective in respect of tolerance to different stresses, improvement in vegetative growth and mineral nutrient status. The benefits of mycorrhiza for micropropagated plantlets have been reported in high value crops such as banana, grapes, oil palm, apple, plum, pineapple, avocado, strawberry, raspberry, cherry, pear, Hortensia spp. and Rhododendron. Reports indicate the root colonization of mycorrhizae during the acclimatization phase, alters root morphology thereby improving the physiology of the plant including water relations, stomatal conductance, levels of total chlorophyll, total soluble sugar, starch, proline, phenol and antioxidant enzymes which helps the plant to overcome transplanting shock along with moisture stress. In addition to this, the beneficial association enhances the ex vitro survival under low input conditions. Physiological and biochemical changes brought about by AMF association render the plantlets to be more resistant against microbial infection and water stress conditions. Reports also reveal that during nutritional stress, AMF plantlets continue to maintain higher N, P and K levels. These indirectly help in improving chlorophyll levels, accelerated photosynthetic rate and stomatal conductance. Due to these changes mycorrhized plantlets showed better growth responses.

Improved plant defense mechanism:
Major shortcomings of tissue cultured plants viz., poor absorption and transportation and sensitivity to microbial infection could be ameliorated with desirable traits of AMF association. Thus, these microorganisms could be used in future alternative biotechnologies for banana production systems. Hardening period of tissue cultured plantlets could be made more economic with the use of mycorrhizal fungi during planting in ex vitro conditions. Biopriming with AMFs not only minimizes extra input in terms of water, fertilizer, pesticides and sophisticated structures like mist chambers but also improves resistance of mycorrhized tissue cultured plants to water and nutritional stress which are generally faced by such plants during transport and during growth periods.

About Author / Additional Info:
Currently working as Scientist in Tissue Culture and Cryopreservation Unit of ICAR-NBPGR