Plant Breeding and Biotechnology

Plant breeding can be conveniently separated into two activities (Kleese & Duvick 1980): manipulating genetic variability and plant evaluation. Historically, selection of plants was made by simply harvesting the seeds from those plants that performed best in the field. Controlled pollination of plants led to the realization that specific crosses could result in a new generation that performed better in the field
than either of the parents or the progeny of subsequent generations, i.e. the expression of heterosis through hybrid vigour was observed. Because one of the two major activities in plant breeding is manipulating genetic variability, a key prerequisite to successful plant breeding is the availability
of genetic diversity (Kuckuck et al. 1991; Villalobos & Engelmann 1995). It is in this area, creating genetic diversity  and manipulating genetic variability, that biotechnology (including tissue-culture techniques) is having its most significant impact. In spite of the general lack of integration of most plant-biotechnology and plant-breeding programmes, field trials of transgenic plants have recently
become much more common. There are therefore reasons to believe that we are on the verge of the revolution, in terms of the types and genetic make up of our crops, that has been predicted for more than a decade (Bodde 1982).

More than 50 different plant species have already been genetically modified, either by vector-dependent (e.g. Agrobacterium) or vector-independent (e.g. biolistic, micro-injection and liposome) methods (Sasson 1993; Anon. 1994). In almost all cases, some type of tissue-culture technology has been used to recover the modified cells or tissues. In fact, tissue-culture techniques have played a majpr role in the
development of plant genetic engineering. For example, four of the seven papers listed by Davis & Reznikov (1992) as classic milestones in plant biotechnology used a range of protoplast, microspore, tissue and organ culture protocols. Tissue culture will continue to playa key role in the genetic-engineering process for the foreseeable future, especially in efficient gene transfer and transgenic plant
recovery (Hinchee et al. 1994).