Model Answer
0 min readIntroduction
Interspecific hybridization, the crossing of plants belonging to different species, is a powerful tool in plant breeding, aiming to combine desirable traits from diverse genetic backgrounds. However, such crosses often result in hybrid embryos that are non-viable due to genetic and physiological incompatibilities. This leads to seed abortion and failure of hybrid development. Embryo rescue is a crucial biotechnological technique employed to overcome this barrier, enabling the recovery and propagation of otherwise lost hybrid embryos. It’s a cornerstone of widening the genetic base of crop plants and introducing novel traits.
Understanding Interspecific Hybridization and its Challenges
Interspecific hybridization aims to transfer beneficial genes, such as disease resistance or stress tolerance, from wild relatives to cultivated crops. However, significant genetic differences between species often lead to:
- Endosperm-Embryo Interactions: The endosperm, which provides nourishment to the developing embryo, may be unable to support the growth of a hybrid embryo due to genetic incompatibility.
- Chromosome Mismatch: Unequal chromosome numbers or structural differences can disrupt meiosis and lead to sterility or developmental abnormalities.
- Seed Abortion: The most common outcome is the abortion of the hybrid seed before maturity.
The Role of Embryo Rescue
Embryo rescue is a in vitro technique that involves the excision of immature embryos from developing hybrid seeds before they lose viability. These embryos are then cultured on a nutrient-rich medium, providing the necessary support for their development into whole plants.
Steps Involved in Embryo Rescue:
- Hybridization: A cross is made between two different species.
- Ovule/Seed Collection: Immature seeds or ovules are collected at a specific stage of development (typically 8-16 days after pollination).
- Embryo Dissection: Embryos are carefully dissected from the ovules under sterile conditions.
- In Vitro Culture: The isolated embryos are placed on a suitable culture medium containing plant growth regulators (auxins and cytokinins) and nutrients.
- Regeneration: Embryos develop into plantlets, which are then transferred to soil for acclimatization and growth.
Applications and Significance
Embryo rescue has been successfully applied in various crop improvement programs, including:
- Wheat-Aegilops Hybrids: Transferring disease resistance genes from Aegilops (wild wheat relatives) to bread wheat.
- Rice-Oryza Hybrids: Introducing traits like blast resistance from wild rice species.
- Brassica Hybrids: Developing novel oilseed varieties with improved quality and yield.
Limitations
Despite its effectiveness, embryo rescue has some limitations:
- Technical Skill: Requires skilled personnel and specialized equipment for embryo dissection and in vitro culture.
- Genotype Dependency: The success rate varies depending on the genetic compatibility of the parent species.
- Somaclonal Variation: Plants regenerated from tissue culture may exhibit genetic variations (somaclonal variation) due to the culture process.
Conclusion
Embryo rescue is an indispensable technique in plant breeding, particularly for overcoming the barriers associated with interspecific hybridization. By rescuing hybrid embryos that would otherwise be lost, it allows breeders to exploit the genetic diversity of wild relatives and develop improved crop varieties with enhanced traits. While challenges remain, ongoing research and advancements in tissue culture techniques continue to refine and expand the applications of embryo rescue in plant improvement.
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.