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Responses to various manipulations, and storage potential, of seeds of the unique desert gymnosperm, Welwitschia mirabilis Hook. fil.
Abstract
The tenacious, dry bracts constituting the coverings
of seeds of the Namib desert gymnosperm, Welwitschia mirabilis, have been shown to impose a constraint on germination
rather than this being a case of physiological dormancy. Removal of these
structures without any other treatment enabled rapid germination, whereas
soaking the seeds either with the coverings intact or removed, resulted in poor
germination. After removal of the coverings, seed samples with a low proportion
of individuals infected by Penicillium crustosum responded well to treatment with a commercial
fungicide (Sporekill®), which eliminated
the fungus, whereas surface-sterilisation with sodium
hypochlorite was extremely damaging. This fungicide, however, was ineffective
when the seed-associated fungus was Aspergillus niger
var. phoenicis.
Germination performance of the seeds was unaffected by their maintenance at
80°C for 48h, establishing both their highly orthodox nature and possibility of
ultra-dry storage, as well as a potential means of thermotherapy. Preliminary
trials established that W. mirabilis
seeds at the water content at which they are shed have the potential to be cryopreserved.
Seeds from which the coverings had been removed not only survived immersion in
liquid nitrogen, but also achieved undimished
germination totality far more rapidly than did the equivalent, untreated
sample. The present work has established the basis of guidelines for the
practical handling of W. mirabilis
seeds and hence conservation of this unique species.
South African Journal of Botany 2004, 70(4): 622–630
of seeds of the Namib desert gymnosperm, Welwitschia mirabilis, have been shown to impose a constraint on germination
rather than this being a case of physiological dormancy. Removal of these
structures without any other treatment enabled rapid germination, whereas
soaking the seeds either with the coverings intact or removed, resulted in poor
germination. After removal of the coverings, seed samples with a low proportion
of individuals infected by Penicillium crustosum responded well to treatment with a commercial
fungicide (Sporekill®), which eliminated
the fungus, whereas surface-sterilisation with sodium
hypochlorite was extremely damaging. This fungicide, however, was ineffective
when the seed-associated fungus was Aspergillus niger
var. phoenicis.
Germination performance of the seeds was unaffected by their maintenance at
80°C for 48h, establishing both their highly orthodox nature and possibility of
ultra-dry storage, as well as a potential means of thermotherapy. Preliminary
trials established that W. mirabilis
seeds at the water content at which they are shed have the potential to be cryopreserved.
Seeds from which the coverings had been removed not only survived immersion in
liquid nitrogen, but also achieved undimished
germination totality far more rapidly than did the equivalent, untreated
sample. The present work has established the basis of guidelines for the
practical handling of W. mirabilis
seeds and hence conservation of this unique species.
South African Journal of Botany 2004, 70(4): 622–630
