Embryo Rescue in Angiosperms: Explanation | UPSC Mains BOTONY-PAPER-I 2020

Embryo rescue in angiosperms.

How to Approach

This question requires a focused explanation of embryo rescue, a biotechnological technique. The answer should define the technique, explain its necessity, detail the process, highlight its applications (especially in wide hybridization), and mention any limitations. A structured approach covering the reasons for its use, the steps involved, and its significance in plant breeding will be effective. Focus on clarity and conciseness within the 150-word limit.

Model Answer

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Introduction

Embryo rescue is a crucial biotechnological technique employed in plant breeding, particularly when dealing with crosses that result in inviable embryos. These crosses, often involving wide hybridization between distantly related species, frequently lead to fertilization and zygote formation, but the resulting embryo fails to develop due to genetic or physiological incompatibilities. This technique circumvents natural barriers to hybridization, enabling the recovery of otherwise lost genetic combinations and broadening the gene pool for crop improvement.

Understanding Embryo Rescue

The primary reason for embryo abortion is often endosperm-embryo incompatibility. The endosperm, providing nourishment to the developing embryo, may be unable to support growth due to genetic differences between the parents.

The Process

Embryo rescue typically involves the following steps:

Timing: Identifying the appropriate stage of embryo development (usually early globular or heart stage).
Isolation: Carefully dissecting the immature seeds and isolating the embryos.
In vitro Culture: Culturing the excised embryos on a nutrient-rich artificial medium under sterile conditions. This provides the necessary support for embryo development.
Regeneration: Allowing the embryos to develop into plantlets, which are then transferred to soil for acclimatization and growth.

Applications

Wide Hybridization: Embryo rescue is extensively used in crossing species like wheat and rye (Triticale) where hybrid embryos are often non-viable.

Overcoming Incompatibilities: It helps in generating viable offspring from crosses between different varieties of the same species exhibiting incompatibility issues.

Haploid Production: Used in conjunction with anther culture to produce haploid plants.

Conclusion

Embryo rescue is a powerful tool in plant breeding, enabling the creation of novel genetic combinations that would otherwise be impossible. While technically demanding, its success in overcoming reproductive barriers has significantly contributed to crop improvement and the expansion of plant genetic resources. Continued refinement of culture techniques and a deeper understanding of embryo-endosperm interactions will further enhance its effectiveness.

Answer Length

This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.

Additional Resources

Key Definitions

Wide Hybridization

Crossing between distantly related plants, often resulting in sterile or inviable offspring due to significant genetic differences.

In vitro Culture

The process of growing cells, tissues, or organs in an artificial environment outside of the organism, typically in a laboratory setting.

Key Statistics

Triticale, a hybrid of wheat and rye, was successfully developed using embryo rescue techniques, with commercial production beginning in the 1970s. It now covers approximately 2% of global wheat area.

Source: FAOSTAT (2023 data, knowledge cutoff)

The success rate of embryo rescue varies significantly, ranging from 5% to 80% depending on the plant species and the degree of incompatibility between the parents.

Source: Plant Breeding Reviews (2019, knowledge cutoff)

Examples

Rice-Wild Relative Cross

Embryo rescue has been successfully employed to cross cultivated rice (Oryza sativa) with its wild relatives to introduce genes for disease resistance and stress tolerance.

Frequently Asked Questions

▶What are the limitations of embryo rescue?

Embryo rescue is labor-intensive, requires specialized skills and equipment, and is not always successful, particularly with highly incompatible crosses. The success rate varies depending on the species and the degree of genetic divergence.