Gene Transfer Methods

Abstract

The ability to alter the genetic composition of a plant is fundamental to crop improvement and development of new cultivars with desirable characters. Plant breeders have utilized the naturally occurring genetic variability in existing germ-plasm to develop new lines by sexual hybridization. In the absence of natural variation for a trait, chemical and radiation mutagenesis was used to create genetic variability for use in the development of varieties with desirable traits. In another approach, genes for superior traits in close relatives were identified and recombined by wide hybridization, thereby generating interspecific or intergeneric hybrids between the donor and target species. However, all these chromosome-mediated gene transfers need sexual hybridizations. Sexual compatibility and chromosome pairing are key components for the introgression of a desired trait. To overcome limited sexual compatibility, embryo rescue using in vitro culture techniques was used to induce genetic variability for desirable traits (Raghavan 1986). The development of protoplast culture and somatic cell hybridization was one of the first examples to create genetic variability by asexual means. Furthermore, in vitro culture of plant cells in suboptimal conditions was found to induce genetic variations termed somaclonal variation, subsequently exhibiting an altered pheno-type (Larkin and Scowcroft 1981). The Agrobacterium tumefaciens-mediated integration of foreign DNA into a cell's nuclear genome and production of a transgenic plant in which the inserted gene was inherited following Mendelian genetics was the ultimate method to create genetic variation across species, irrespective of genetic proximity or sexual compatibility (Otten et al. 1981).