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The following points highlight the top six applications of embryo culture. The applications are: 1. Rescuing Embryos from Incompatible Crosses 2. Overcoming Dormancy and Shortening Breeding Cycle 3. Overcoming Seed Sterility 4. Embryo Callus has Organogenic Potential 5. Production of Monoploids and Diploids 6. Biotechnological Application.
Application # 1. Rescuing Embryos from Incompatible Crosses:
In case of interspecific or inter-generic crosses there may be normal fertilization but the embryo abortion results in the formation of non-viable seeds. Of several cases studied, poor or abnormal development of endosperm caused embryo starvation and eventual abortion.
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In these cases the hybrid embryos can be isolated before abortion and can be cultured into a cellular endosperm of anyone of the parents or using the endosperm of any closely related third species. This technique is called embryo-endosperm and transplant technique (Fig. 19.2).
Isolation of hybrid embryos at the immature stage i.e., before abortion and their culture in vitro may circumvent strong post-zygotic barriers. To raise the rare hybrids by rescuing embryos from incompatible crosses is the most popular application of embryo culture. With the improvement of embryo culture technique a large number of interspecific and inter-generic hybrid plants have been raised.
Application # 2. Overcoming Dormancy and Shortening Breeding Cycle:
Long periods of seed dormancy may lead to delay in breeding work in horticultural and crop plants. Using embryo culture technique the seed dormancy can be overcome. Seed dormancy may be caused by some metabolic inhibitors produced within the seed or due to presence of hard seed coat.
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In these cases the mature embryo culture is the best way to overcome seed dormancy. But when the cause of seed dormancy is not well understood, the immature embryos are excised and cultured to by-pass the seed-dormancy.
Application # 3. Overcoming Seed Sterility:
In early ripening fruit cultivars, seeds do not germinate because their embryo remains still immature. Using embryo culture method it is possible to raise seedlings from sterile seeds of early ripening stone fruits.
Application # 4. Embryo Callus has Organogenic Potential:
An embryo callus is reported to possess a high regenerative capacity compared to those derived from mature organs such as the leaf, stem and root. The age of embryo influences the regenerative ability of callus.
Generally no differentiation occurs in case of callus obtained from mature embryo but the immature embryos of many monocots can be of potential use for production of callus which may be used as good explants to initiate the plant regeneration through organogenesis. To obtain a callus with morphogenic potential excised embryos are placed on an agar medium with the scutellum facing up in the presence of 2, 4-D alone or in combination with cytokinin.
Application # 5. Production of Monoploids and Diploids:
Embryo culture technique has been used to raise the monoploids in barley, where the interspecific fertilization between Hordeum vulgare and H. bulbosum takes place but during further development one chromosome set gets eliminated, resulting in the formation of monoploid of barley which can be rescued by embryo culture.
When a tetraploid and a diploid species are crossed to get the seedless triploid plant (as in case of Citrus) the embryo culture through rescuing of immature embryos is important.
Application # 6. Biotechnological Application:
Plasma membranes of desiccated zygotic embryos are generally with large pores. The mature embryos in excised condition can be soaked or imbibed in a solution containing the vector DNA with desirable clone, which can enter within the cell and get transformed within the embryonic cell and can be perpetuated within the developing embryo.
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Another method is application of biolistic method i.e., by using particle gun the DNA clone can be pushed within the embryonal tissue which can be transformed easily and can produce the plant with transformed clones.
