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Storage and Germination Response of Recalcitrant Seeds Subjected to Mild Dehydration

S. Eggers, D. Erdey, N.W. Pammenterand P. Berjak

School of Biological and Conservation Sciences, University of KwaZulu-Natal, Durban 4041, South Africa

A problem associated with the storage of fully hydrated recalcitrant seeds is germination in storage, and it has been suggested that this problem could be overcome by partial dehydration, which is sufficient to prevent germination but high enough to avoid desiccation damage (i.e. 'sub-imbibed' storage). However, partial drying (pd) is shown to stimulate germination, and this process could reduce storage lifespan. Data are presented on recalcitrant seeds from a number of species, demonstrating the enhancement of germination by rapid mild dehydration, and the adverse effects of this mild dehydration on subsequent storage at a range of temperatures.

Recalcitrant seeds, by definition, are desiccation-sensitive and hence cannot be stored by the conventional methods employed for orthodox seeds. Not only does this make the long-term conservation of their genetic resources difficult, but it also places limitations on normal seed-handling procedures. To date the only 'successful' way of storing recalcitrant seeds is in the hydrated condition, at their shedding water content, but storage lifespan varies from several months, at best, to a week or two, depending on the species and the physiological condition of the seeds (King and Roberts, 1980). There are two main problems that are associated with hydrated storage: (i) seeds will often germinate in storage (King and Roberts, 1980); and (ii) the effects of fungal contamination can be severe, as the conditions (i.e. high humidity and temperature) necessary for hydrated storage also favour fungal proliferation (Mycock and Berjak, 1990).

Recalcitrant seeds are metabolically active (Berjak et al., 1984; Farrant et al., 1997), undergo continued development after shedding that grades into germination-associated

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