1 John H. Dodds The culture offragmen ts of plant tissue is not a
particularly new science, in fact as long ago as 1893 Rechinger (1893)
described the formation of callus on isolated fragments of stems and
roots. The culture of plant tissues in vitro on a nutrient medium was
performed by Haberlandt (1902), however, his attempts were unsuccessful
because he chose too simple a medium that lacked critical growth
factors. Over the last fifty years there has been a surge of development
in plant tissue culture techniques and a host of techniques are now
avail- able (Dodds and Roberts, 1982). The major areas are as follows.
Callus Culture Callus is a rather ill-dermed material. but is usually
described as an un- organised proliferating mass of tissue. Although
callus cultures have a great deal of potential in the biotechnological
aspects of tissue culture, i.e. secondary product formation, they are
not very suitable for plant propagation. The key reason for their
unsuitability is that genetic aber- rations occur during mitotic
divisions in callus growth (D'amato.l965). The aberrations can be of a
major type, such as aneuploidy or endo- reduplication. It follows
therefore that the genetic status of the re- generated plants is
different from that of the parent type. In general terms this genetic
instability is undesirable, but there are occasions when a callus stage
can be purposely included to diversify the genetic base of the crop.
