Protocols for Micropropagation of Woody Trees and Fruits

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2.8. Hardening
V. RAJESWARI AND K. PALIWAL
Remove plantlets, which have attained the height of about 4–5 cm from culture
vessels. Wash the root system thoroughly in running tap water to remove traces of
medium adhering to the plantlet. Transfer the individual plantlets into small plastic
pots (10 cm diameter) containing sterilized vermiculite moistened with half strength
MS medium without sucrose (Figure 4G). To retain high humidity cover the potted
plantlets with clear plastic sheet and keep under culture room condition. After 1-month
transfer plantlets to polybags (15 × 25 cm) containing soil, sand and farmyard manure
in the ratio of 3:1:1 and keep in a shade house.
3. CONCLUSION
This chapter described a reliable and reproducible micropropagation protocol for
Albizia odoratissima based on axillary shoot proliferation as well as adventitious
shoot organogenesis from seedling explants. The results have shown that the efficiency
of micropropagation system is influenced by both the physiological state of the
donor plants and also by the type of explants. This is evident in the present study
that the number of shoots produced by the explants of more juvenile source (14-dayold
seedling) was more than that of the older explant source (two-year-old sapling).
Even though the clonal propagation system developed for the matured tree is much
more valuable than the juvenile seedlings, this study is conducted primarily to
generate information on the nature of responses exhibited in vitro by the tissues of
this plant which can be extended to studies with mature explants. As most of the
woody species segregate for phenotypic traits when propagated by seeds, the plants
regenerated in vitro from seedling explants would display inherent genetic variation.
This could, however, be controlled by using an elite seed population as was selected
by Pradhan et al. (1998) for their study on propagation of Dalbergia latifolia. The
method developed for adventitious shoot organogenesis permits the rapid rate of plant
production and histological analysis showed that the shoot buds originated from
cambial cells thus minimizing the risk of producing genetically off types.
Cloning of mature trees through tissue culture is generally preferred to that of
juvenile tissue as it is not always possible to determine if the juvenile tissue will
have the desired qualities at maturity. However, explants derived from mature trees
show inherent recalcitrance to in vitro condition. Therefore, improvements and
refinements in the technique will be necessary. The cost per plant would be high
particularly if one considers application of this method for mass propagation. Development
of somatic embryos and encapsulation with enriched polymers and production
of synthetic seeds could be a solution to this problem of economics of micropropagation.
New developments in genetic engineering procedures, including the recent
somaclonal, gametoclonal and embryo rescue technologies show promise for their
inclusion and applications in tree breeding programs for the genetic improvement of
forest tree species. These technologies when combined with the methods of
micropropagation for raising seed orchards could greatly reduce the time normally
taken in conventional tree breeding programs.