Cryopreservation for germplasm exchange — Which materials have been successfully cryopreserved with ~90% tissue survival and ~10% whole-plant regeneration, and are widely used for international germplasm exchange?

Introduction / Context:
Cryopreservation enables long-term, pathogen-safe exchange and conservation of elite germplasm. Two commonly used explant types are meristem tips and embryos, which tolerate cryogenic protocols and can regenerate plants following thawing.

Given Data / Assumptions:

• Reported outcomes include high tissue survival (~90%) and modest yet practical plant regeneration (~10%).
• Virus indexing is facilitated by meristem tips; embryos are useful across many species.
• Standard cryo-methods include vitrification, encapsulation-dehydration, and controlled-rate cooling.

Concept / Approach:
Both meristem tip cultures and embryos have favorable surface area, metabolic status, and size for successful dehydration/vitrification and recovery. Hence, both are utilized worldwide in exchange systems and genebank operations.

Step-by-Step Solution:

Verification / Alternative check:
International genebanks and tissue culture repositories document routine cryostorage of shoot tips and zygotic embryos with recovery to plantlets under optimized media.

Why Other Options Are Wrong:

Common Pitfalls:
Neglecting pre-culture and dehydration steps; inadequate osmoprotection reduces survival.

Final Answer:
Both (a) and (b).