Recalcitrant seed

Recalcitrant seeds refer to a category of seeds that do not survive drying and freezing during ex-situ conservation. Unlike orthodox seeds, which can be dried to low moisture contents and frozen without significant damage, recalcitrant seeds lose viability if they are dried below a certain moisture level or exposed to low temperatures. This characteristic makes the long-term storage and conservation of recalcitrant seeds a significant challenge in the fields of botany and conservation biology.

Characteristics

Recalcitrant seeds are typically large, with high moisture content and are often found in tropical and subtropical species. They are metabolically active and cannot enter a state of deep dormancy. Due to their sensitivity to desiccation and cold, recalcitrant seeds must be stored in conditions that mimic their natural environment, which often involves maintaining them at high moisture levels and temperatures above freezing.

Examples

Some well-known examples of plants that produce recalcitrant seeds include:

• Mangifera indica (Mango)
• Hevea brasiliensis (Rubber tree)
• Theobroma cacao (Cocoa)
• Aesculus hippocastanum (Horse chestnut)
• Several species of oak (Quercus spp.)

Conservation Challenges

The recalcitrant nature of these seeds poses significant challenges for seed banks and conservationists. Traditional seed banking methods, which involve drying seeds to low moisture content and storing them at sub-zero temperatures, are not suitable for recalcitrant seeds. Instead, alternative strategies such as cryopreservation (freezing seeds at very low temperatures using liquid nitrogen) are being explored, although this method is not yet widely applicable for all recalcitrant seed species due to technical and cost-related issues.

Research and Techniques

Research in the field of recalcitrant seed conservation focuses on understanding the physiological and biochemical basis of seed recalcitrance, developing storage methods that can maintain seed viability, and exploring the genetic basis of desiccation sensitivity. Techniques such as partial drying, where seeds are dried to the lowest possible moisture content without losing viability, and encapsulation-dehydration, where seeds are encapsulated in a protective medium before drying, are among the methods being studied to extend the lifespan of recalcitrant seeds.

Conclusion

Recalcitrant seeds represent a significant challenge to global conservation efforts, particularly as many species with recalcitrant seeds are of economic and ecological importance. Advances in research and the development of new conservation techniques are critical to ensuring the survival of these species in the face of environmental change and habitat loss.