Dormancy, germination and seedling growth of two Kalaharian perennials of the genus Harpagophytum (Pedaliaceae)

Abstract

Dormancy and germination ecology of two Harpagophytum species (Pedaliaceae) from an open Acacia savanna in Botswana were investigated. The maintenance of dormancy is governed partly by the seed coat but mainly by the endosperm and the embryo itself, as demonstrated by removal of the endosperm. Dissemination of the seed from the fruit can be delayed for several years without affecting the viability of the embryo, due to very low respiration rates.Germination can be enhanced slightly by high temperatures under natural conditions, and by gibberellic acid or removal of the endosperm under laboratory conditions. Relative growth rates for both Harpagophytum species are lower than for subtropical grasses and legumes, due to a strong investment in root and tuber biomass. Germination and seedling growth is discussed in relation to the drought avoidance syndrome and the animal disperser syndrome.

Micropropagation of Harpagophytum procumbens

“…Out of these pretreatments tried, the seeds, which were pricked at the basal end and soaked in GA 3 overnight responded well. Ernst et al (1988) also reported the positive influence of GA 3 for seed germination of two Harpagophytum species. The soaked seeds were then surface-disinfected with 0.1 % HgCl 2 (m/v) for 3 min, followed by 3 washes in sterile distilled water, and transferred to half-strength MS basal medium (Murashige and Skoog 1962) containing 1 % (m/v) sucrose and 0.8 % (m/v) agar.…”

“…Due to its high medicinal importance (Van Haelen et al 1983), rural communities intensively harvest the species in the field. Furthermore, the seeds exhibit a high degree of dormancy (Ernst et al 1988) resulting in very poor seedling recruitment. Plant tissue culture techniques provide a suitable alternative method for mass propagation of this endangered species (Levieille and Wilson 2000, 2002, Afolayan and Adibola 2004.…”

The commercial harvest of devil's claw (Harpagophytum spp.) in southern Africa: The devil's in the details

“…The flattened woody capsules, which give the plant its scientific and common names, bear two rows of curved arms studded with curved spines (Harpagophytum literally means grapple hook plant). The fruit is animal dispersed (Ernst et al, 1988), because it easily entangles itself in animal fur or wool, although it appears to be wind dispersed to some degree, as a breeze can carry a fruit for some distance from the parent plant. Seeds have a high degree of dormancy (Veenendaal, 1984;De Jong, 1985), which may be an adaptation to drought (Ernst et al, 1988).…”

“…The fruit is animal dispersed (Ernst et al, 1988), because it easily entangles itself in animal fur or wool, although it appears to be wind dispersed to some degree, as a breeze can carry a fruit for some distance from the parent plant. Seeds have a high degree of dormancy (Veenendaal, 1984;De Jong, 1985), which may be an adaptation to drought (Ernst et al, 1988). In addition, seeds are released slowly from the mature fruit.…”

“…In addition, seeds are released slowly from the mature fruit. Ernst et al (1988) estimates that in a given year, only 20-25% of the seeds within a fruit may establish soil contact, and he suggests this is an adaptation to animal (or wind) dispersal. Further, he estimates that, since seeds have a low respiration rate, they can remain viable in the seed bank for more than 20 years.…”