INTEGRATION OF ARBUSCULAR MYCORRHIZAL
TECHNOLOGY WITH MICRO-PROPAGATION

One of the important applications of modern biotechnology in agriculture is its use in tissue culture. In vitro micropropagation techniques are increasingly being applied to large scale production of quality planting materials especially in fruit crops and woody timber trees. There are four important stages in the micropropagation of plants irrespective of the various techniques employed for it. They are the regeneration in in vitro, proliferation of the regenerates, rooting in in vitro and for transplantation of the plantlets in the soil or fields. Of these, the last stage is very crucial and important with respect to the establishment of the in vitro derived plantlets. It has been established that tissue culture plantlets have very divergent leaf anatomy and physiology and hence require an acclimatization period during the transition from culture to green house, from a total unnatural system to the very natural environment. In the in vitro condition, plantlets are heterotrophic and get very high favourable conditions for their growth. But in the ex vitro situation, the plantlets have to switch over to autotrophic nutrition, involving normal photosynthetic activity and water relations. The plantlets may not be able to withstand such sudden shocks of the environmental changes, mostly due to some aberrant characteristic features of in vitro derived plantlets.

Physiological features of tissue culture plantlets

One of the major impediments to the success of micropropagation is the very high mortality rate of in vitro plantlets either during acclimatization phase or during transfer to the field conditions. Generally, most of the in vitro derived plantlets fail to survive. Very often desiccation and wilting are the main causes of low survival. It has been estimated that roughly only 25 percent of the in vitro regenerated plantlets has been successfully transplanted ex vitro and still fewer transferred to the field. Such a disappointing state of affairs has been attributed to certain underlying causes, of which the aberrant features characteristic of in vitro derived plantlets are significant. Some of such features are as follows.

1. Leaves with poor or no development of cuticular wax:

The high humidity in the culture vessels hinders the development of cuticle and epicuticular wax on the newly emerging leaves. When such plantlets are planted out they undergo desiccation and drying. It has been noticed that the palisade cells of leaf surface are poorly developed and pronounced mesophyll airspaces.