182 W. A. VENDRAME AND A. A. KHODDAMZADEH
Table 4.1 lists some relevant micropropagation studies with orchids in
addition to those mentioned here.
When describing the different micropropagation techniques used for
orchids, the induction of PLBs has been used as an important and main-
stream technique. However, specifically for orchids, the terms PLBs and
somatic embryos have been used interchangeably and as synonyms in
the literature (Chen and Chang 2000a, 2000b, 2001; Teixeira da Silva
2003; Chen and Chang 2004a, 2004b, 2006; Teixeira da Silva and Tanaka
2006; Zhao et al. 2011; Teixeira da Silva et al. 2015). To settle the ques-
tion and avoid subsequent confusion, a detailed study performed by Lee
et al. (2013) compared PLBs with somatic embryos and zygotic embryos
and demonstrated that during early stages of PLB development cells are
similar to zygotic embryo development, therefore justifying that orchid
PLBs are in fact somatic embryos.
Generally, tissue culture technology offers many unique benefits in
comparison with conventional propagation techniques such as rapid
multiplication of valuable plant material, year round production, fast
release of improved varieties, germplasm conservation, and the facil-
itation of international exchange of plant material (Govil and Gupta
1997), since it provides safeguards that lower risks of diseasesviaclean,
pathogen-free plant material. The plant material is grown on a well-
defined agar medium that contains all the nutrients and plant growth
regulators required for plant growth and development. In the specific
case ofPhalaenopsis, a monopodial orchid, it rarely produces offshoots
and is difficult to propagate vegetatively (Ishii et al. 1998; Young et al.
2000). Different plant parts such as rhizome, root tips, buds, flower
stalks, and shoot tips (Tanaka et al. 1975; Arditti and Ernst 1993; Chen
and Piluek 1995; Park et al. 2002a; Chen et al. 2004) have been used for
in vitropropagation ofPhalaenopsis. Among different explants, foliar
explants have the advantage of preserving the mother plant (Chugh et al.
2009). Park et al. (2002b) additionally reported the use of leaf segments
to induce PLBs in differentPhalaenopsishybrids. Furthermore, leaf seg-
ments were also used to induce PLBs inOncidesaGower Ramsey (Chen
and Chang 2004b)
Organogenesis can be exploited for micropropagation of orchids and
is defined as the appearance of a new organ, initially a protrusion, at
the site where only a parent structure is present (Roostika and Mariska
2003). Shoot organogenesis refers to propagation from explants with-
out pre-existing meristems through production and subsequent rooting
of adventitious shoots. Shoot organogenesis can be direct or indirect.
Direct shoot organogenesis is the production of shoots directly from
explants, while indirect refers to the formation of shoots from explants