So, effective control agents (usually chemical
agents) exist for most plant diseases, except those caused
by viruses. The main reason for use of the meristem culture
is the fact that most viruses do not attack the meristem
of shoots, since the multiplication of meristem cells
is faster than replication of viruses, although more recent
studies have shown that the mechanism of gene silencing
is in fact the main reason (Foster et al., 2002).
Meristem culture is a procedure which does not differ
in general from procedures for shoot reproduction
in vitro. However, an important requirement is that initial
explants be as small as possible in order to be able to
isolate only the apical meristem, rather than permanent
cells containing viruses. Morel and Martin (1952) first
demonstrated the elimination of viruses from Dahlia
using meristem culture. Since then, the use of meristem
culture to obtain virus-free ornamental plants has been
widely used by numerous groups of researchers (Table 1).