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The following points highlight the seven main methods to introduce the better characters in plants. The methods are: 1.Tissue Culture Technique 2.Cell Fusion 3. Somatic Cell Hybridization or Cytoplast or Cybrid 4. Somaclonal Variations 5. Organ Culture Technique 6. Embryo Rescue 7. Genetic Engineering.
Method # 1. Tissue Culture Technique:
Plant tissue culture technique is used to select somaclones that are resistant to herbicides. The plants in which herbicidal resistance has been selected for tissue culture is limited to few species.
Method # 2. Cell Fusion:
Proplasts from different cells are made to fuse by treating them with certain chemicals or electric current. By this method chromosomes of different species can be combined particularly in those species which are otherwise incompatible.
Method # 3. Somatic Cell Hybridization or Cytoplast or Cybrid:
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Power et. al. (1970) crossed oat with maize by this technique. Usually by protoplast fusion heterokaryon is formed, without the fusion of nuclei. One or both the nuclei may be lost later on. Sometimes one nucleus is left in the mixture of both the cytoplasms. This product is called Cytoplast or Cybrid. The study of cybrids is proving useful for investigation of possible recombination within extrachromosomal genomes.
Method # 4. Somaclonal Variations:
The method refers to heritable changes which accumulate in callus from a somatic explant and express in the progeny of in vitro regenerants obtained from callus. Somaclonal variations have been found to be taking place both for nuclear and cytoplasmic origin.
Method # 5. Organ Culture Technique:
The technique is being used to culture isolated embryos. This is being done in those cases where viable zygotes are produced but due to incompatible genie interactions normal embryo and endosperm formation is checked.
Method # 6. Embryo Rescue:
Sometimes embryo formed in various crosses suffers from post fertilization development inhibitory actions. Due to this normal viable seeds are not formed. Such hybrid embryos can be saved by growing them in artificial media.
Method # 7. Genetic Engineering:
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It promises rapid acceleration of plant breeding efforts for crop improvement. Some success has been achieved in developing varieties resistant to herbicides, viral diseases and insect pests.
