Embryo Rescue Methods and their Applications | Botany Optional for UPSC PDF Download

Embryo Rescue

Embryo rescue is a method used to safeguard underdeveloped, fragile, and hybrid embryos, facilitating their growth into healthy plants. It is one of the earliest successful techniques in the realm of in vitro and tissue culture.
The history of embryo rescue dates back to the 18th century when Charles Bonnet effectively removed embryos from Phaseolus and Fagopyrum plants and successfully transplanted them into the soil. Subsequently, numerous scientists experimented with various nutrient media to refine the process. Between 1890 and 1904, embryo rescue was explored using nutrient solutions containing salts and sugars in conjunction with tissue culture techniques.
In 1904, Hanning achieved a breakthrough by successfully initiating embryo growth in tissue culture. However, he encountered challenges with premature or early embryos, which resulted in the development of stunted and frail seedlings.
Embryo rescue holds significant importance in the field of plant breeding, allowing the nurturing of feeble embryos, particularly those resulting from crosses between different species or genera, into fully developed plants.
In natural settings, embryos produced from interspecific or intergeneric crosses often remain underdeveloped and fail to develop into mature plants. In cases involving incompatible plant crosses, these embryos are typically aborted. Tissue culture techniques, including embryo culture, come to the rescue in such situations, enabling the cultivation of diverse hybrid plants.

Embryo Culture 

Embryo culture is a widely employed technique for rescuing embryos, and it is commonly used in plant breeding. This method involves the collection of seeds from controlled pollination plants before the embryos are expected to naturally terminate their development. Subsequently, the embryos are carefully isolated and removed under sterile conditions, after which they are directly placed on a culture medium to encourage the growth of viable plants.

Embryo culture can be categorized into two types based on the developmental stage of the embryos introduced into the culture medium:

• Mature Embryo Culture: This process entails the cultivation of fully mature and ripe embryos in controlled laboratory conditions. It is employed when embryos struggle to survive under natural, in vivo conditions, remain dormant for extended periods, or face hindrances to germination.
• Immature Embryo Culture: This method is used to culture immature, fragile, or small embryos that would not typically develop into hybrid plants due to endosperm degeneration in natural settings. This approach is often referred to as embryo rescue because it involves nurturing and promoting the development of these embryos into fully grown plants through in vitro culture techniques.

Factors that Influence the Embryo Culture

• Medium Composition: Typically, embryo culture employs one of two types of media: Murashige and Skoog media (MS media) or Gamborg's B-5 media. Nevertheless, adjustments to the media supplements are often necessary. For instance, young embryos may require a higher sucrose concentration, whereas mature embryos may thrive with lower sucrose levels.
• Culture Timing and Embryo Development Stage: It is recommended to culture embryos prior to their natural abortion. However, due to challenges in obtaining and nurturing very early-stage embryos, they are sometimes allowed to grow as much as possible in their natural, in vivo environment.
• Temperature: The appropriate temperature for embryos varies depending on the plant species. Cold-season plants typically require lower temperatures, while those from warmer seasons tend to thrive at higher temperatures.

Applications of Embryo Culture

Embryo culture is used for several breeding purposes, some of which are explained below:

• Facilitating hybridization between diploid and tetraploid organisms.
• Assessing the viability of seeds.
• Crossbreeding incompatible species from different genera or interspecific crosses.
• Accelerating the breeding cycle of deciduous trees.
• Investigating the physiological aspects of seed germination and growth.
• Propagating plants, particularly conifers and members of the Gramineae family, through in vitro methods.
• Exploring nutrient needs and the process of morphogenesis.
• Initiating the germination of seeds from obligatory parasites in the absence of their host organisms.

Other Techniques of Embryo Rescue

Aside from embryo culture, other techniques available for embryo rescue, particularly for plant species with small seeds or young embryos, include ovary and ovule culture.

• Ovary Culture: In this approach, flowers from pollinated or non-pollinated plants are carefully removed, and the ovary within the pistil is isolated and placed on a nutrient medium to encourage the complete regeneration of plants. This method is also referred to as gynogenesis.
• Ovule Culture: In this method, the ovule is aseptically extracted from the ovary and cultured on a chemically defined nutrient medium under controlled conditions. This technique aids in studying the factors that govern the development of a zygote into a mature embryo.

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