Viable seeds are produced by the plants after intraspecific crosses i.e. cross between two similar species. On the other hand, if inter-specific cross (cross between two different species) and intergenic cross (cross between two genera) occurs; no viable seed develops in the ovary.

It is due to abnormal development of endosperm which results in death of embryo before maturity and sterile seed formation. Besides, there are other barriers also which operate during the stage of pollination or fertilisation.

However, in some cases in spite of pollination and fertilisation, embryo does not develop. This is due to incompatibility between the developing embryo and endosperm.

From such sterile hybrid seeds, immature embryo can be taken out and grown on artificial medium.

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Such pre-mature embryos differentiate into shoot, root and plantlets. This technique of culturing immature embryo on artificial nutrient medium is called embryo rescue.

Embryo rescue technology is very useful now-a-days for regenerating plants from the embryos formed after interspecific or intergenic crosses.