Plant Propogation and Nursery Management

Stages of Micropropagation

Micro propagation is an integrated process in which cells, tissues or organs of the selected plants are isolated, surface sterilized and incubated in growth promoting, sterile medium and environment to produce a large number of plants. The different stages are:

Stage 0: Selection of mother plant for explants isolation: The mother plant from which explants has to be excised should be

a.) A certified and true to type representative of the desired species and or cultivar.
b.) Healthy and free from insect pest and disease
c.) Should be quite vigorous.

Stage1: Explant establishment in culture medium: During this stage the explant is cultured in a suitable culture medium, preferably agar based media for tissue activation and multiplication.
Stage2: Proliferation and multiplication: In this stage, repeated sub-culturing is done to encourage more proliferation, which largely depends upon the combination of growth regulators (Plate 13.1). The duration of this stage is unlimited and largely depends on the choice of propagator.
Stage 3: Plant establishment and rooting: In this stage the selected plants are forced for root formation, which can be achieved by media modification and modifying the concentration of growth regulators. The concentration of cytokinins and sugars are reduced and concentration of auxins and light intensity in the laboratory is increased to start with photosynthesis and other physiological activities.



Plate 13.1 Proliferation and multiplication of plants

Stage 4. Acclimatization or hardening: The plantlets developed in the culture tubes are acclimatized to specific environment having a high humidity, a low light level and a constant temperature (Plate13.2). Besides, the roots developed in vitro are hairless and hence delicate, requiring care during transfer from culture medium. To have better survival rate, the plantlets may be transferred to container kept in mist chambers where relative humidity is maintained at higher order. Once new growth is seen, the plants may be slowly transferred to outside by exposing to increased light intensity in stages.



Plate 13.2. Hardening of tissue culture plants

Once plantlets are well rooted, they must be acclimatized to the green house environment. In vitro rooted plants are removed from the culture vessel and the agar is washed away completely to remove a potential source of contamination. Plantlets are transplanted into a standard pasteurized rooting or soil mixture in small pots or cells in a more or less conventional manner as shown in Plate 13.3. Initially, micro-plants should be protected from desiccation in a shaded, high humidity tent or under mist or fog. Several days may be required for new functional roots to form.



Plate 13.3 Hardening of plants

Plantlets should be gradually exposed to a lower relative humidity and a higher light intensity. Any dormancy or resting condition that develops may need to be overcome as part of the establishment process. These conditions help the plantlets in getting acclimatized to the natural conditions, which would help them in getting established in the field easily.