Liquid Culture Systems for in vitro Plant Propagation

390 Pramod K. Gupta & Roger Timmis
potential as a method for mass propagation of superior conifer genotypes. It
potentially provides many production advantages:
1. A large number of plantlets can be produced inexpensively.
2. Production of both root and shoot meristem occur in the same process
step.
3. Easy and quick scale-up can be achieved via liquid culture.
4. Long term storage via cryopreservation can be utilized.
5. There are opportunities for use of manufactured seeds for direct delivery
to a nursery and easy handling.
In forestry, the production of manufactured seeds throughout the year
provides a complementary technology, which will reduce risks relative to
seed orchards where seed production is limited and variable.
Considerable progress has been made over the last decade in the
development of somatic embryogenesis systems for large-scale clonal
propagation of conifers. Since the first report in 1985, a large number of
papers have been published on development of protocols for somatic embryo
development, maturation, germination and cryopreservation of several
conifer species (Gupta et al., 1993, Gupta and Grob, 1995, Timmis 1998).
Several patents have been granted to forest industries and universities on
conifer somatic embryogenesis technology. Weyerhaeuser Company also
has several patents on this technology. Commercialization of this technology
consists of the following steps:
1. Initiation of ESM (embryonal suspensor mass) from a large number of
genotypes of selected families.
2. Multiplication of ESM cultures in liquid medium.
3. Cryopreservation of ESM cultures.
4. Production of somatic seedlings for clonal field-testing.
5. Development of an efficient low cost delivery system to nurseries.
6. Collection of data from clonal field-tests.
7. Retrieving the ESM of field-tested clones from cryostorage.
8. Scale-up of ESM cultures for large-scale production of somatic seedlings
and clonal reforestation.
This paper describes all of the above steps and scale-up in liquid media for
mass clonal propagation using somatic embryogenesis technology.
2. Culture initiation and maintenance
Induction of embryo suspensor masses (ESMs) has been reported from
immature embryos, mature embryos, hypocotyls, cotyledons, and explants of
somatic and zygotic seedlings of Norway spruce (Picea abies). Recently,
ESM induction has also been reported from explants of 10-20-year-old trees