TISSUE CULTURE TECHNIQUES FOR TREE SPECIES

Embryo Culture

In traditional plant breeding, hydrid embryos of many interspecific crosses fail to grow to maturity mainly due to the degeneration of the endosperm or an abortion of the embryos has now found wide utilization in the fruit trees. It has been successfully used for peach, plum, pear and apple cultivars. Another application of embryo culture is to overcome seed dormancy which with many trees take several years for germination under natural condition.

Anther Culture

Haploid plants being gametophytic in origin possess only half the normal number of chromosomes as present in the parent. They can be used to produce homozygous lines which are invaluable for any breeding programmes and also for various other genetic manipulation. After the first successful report on regeneration of haploid plants from pollen grains of the cultured anthers of datura this technique has been demonstrated in a large number of herbaceous species. However, the technique of culturing anthers and pollen has found only limited success when applied to forest species. Haploid callus has been obtained from cultural anthers of forest tree species of Pinus, Vitis, Citrus, etc.

Early Induction of Flowering to Shorten to Breeding Cycle

Trees unlike agricultural crops, take years to attain sexual maturity and to flower. Thus, tree breeders have to wait up to twenty years or even more. This problem is further aggrevated in some trees such as bamboo, which may flower once in forty years. Thus the early induction of flowering by the application of growth regulators in vivo or their use in in vitro cultures would help to reduce the breeding cycle.

Somatic Hybrids through Protoplast fusion

Somatic hybridization through protoplast fusion opens an avenue for synthesizing characteristics which were not possible hitherto. Even in wide crosses through embryo cultures, the degree of variability is low. Somatic hybridization is an alternative to sex in order to combine the entire genomes from incompatible parents and is expected to result in hybrids.

Transformation through uptake of Foreign genomes

Genetic transformation using Agrobacterium mediated transfer is another important technique in which a gene or group of genes encoding for a specific trait can be isolated and cloned.