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Literature review
In stage II or the propagation phase explants are cultured onto a medium that
promotes the multiplication of shoots (AHLOOWALIA et al., 2002). Propagation must
be achieved without excessive mutation (AHLOOWALIA et al., 2002). The culture of
various organs in stage I lead to the multiplication of propagules in large numbers.
These propagules can be cultured further and used for multiplication (AHLOOWALIA
et al., 2002). These cultured shoots are often placed onto different media for
elongation (AHLOOWALIA et al., 2002).
The result of stage III is the production of complete plants, as the shoots derived from
stage II are rooted (AHLOOWALIA et al., 2002). If shoot clumps are present, they
should be separated after rooting. Many plants can be rooted on half strength
Murashige and Skoog medium without any growth regulators (AHLOOWALIA et al.,
2002). Successful and sufficient rooting is essential for survival of the plant during
hardening and transfer to the soil (AHLOOWALIA et al., 2002).
The complete plants are weaned and hardened during stage IV (AHLOOWALIA et
al., 2002). The plants should at this stage be autotrophic. Hardening consists of
gradually altering the humidity, light and nutrition available to the plant. The plant is
moved gradually from a high to a low humidity, from a low light intensity to a high
light intensity and the agar is removed by gently washing it away with water. After
sufficient hardening, plants can be transplanted to a suitable substrate and hardened
further (AHLOOWALIA et al., 2002).
In vitro regeneration techniques are essential to the application of in vitro selection
techniques (REMOTTI & LÖFFLER, 1995). This is not only because it enables the
selected genotype to be regenerated, but also it aids commercialisation of new
species and selected genotypes (DEBERGH, 1994).
Micropropagation enables the production of disease free plantlets at high rates and
generally increases the efficiency of known breeding techniques (DEBERGH, 1994).
It is also essential in the breeding of plants for which no breeding methods or
procedures have been established (DEBERGH, 1994). In vitro selection techniques
have been used to increase genetic variability and to broaden the gene pool
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