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South African Journal of Botany 67 (2) 2001, 79–89
©2001 NISC Pty Ltd, www.nisc.co.za
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Seed recalcitrance — current perspectives
P Berjak* and NW Pammenter
School of Life and Environmental Sciences, University of Natal, Durban 4041, South Africa
* Corresponding author, e-mail: [email protected]
Received 19 February 2001, accepted in revised form 26 February 2001
The phenomenon of non-orthodox seed behaviour is presented in the framework of the probability of being much more common than might be expected, considering that scientific knowledge about seeds is largely drawn from what has been established for a mere handful of cultivated crop species. The scattering of species producing recalcitrant seeds across most angiosperm families (and among the gymnosperms) appears to have no taxonomic basis, although recalcitrance might be the ancestral seed condition. Recalcitrance is considered not as deviant, but rather as one extreme of a continuum of seed behaviour based on the response to dehydration, the other extreme being manifested by those orthodox seeds that are able to tolerate almost total desiccation. Post-harvest seed responses to dehydration are presented in the context of developmental events that characterise pre-shedding development. Those that acquire desiccation tolerance and will survive lengthy periods in the desiccated state do so as a result of the full development and interaction of a suite of mechanisms enabling this competence. Highly recalcitrant seeds which consistently remain metabolically active, are considered not to possess, or express, most or all of these, while inbetween the extremes of recalcitrance and orthodoxy, seeds that might be considered as non-orthodox (but also not recalcitrant) will manifest these mechanisms and their interactions variably — thus accounting for a continuum of seed behaviour in the context of relative desiccation tolerance. Emphasis is laid on the fact that the degree of dehydration tolerated by seed tissues is a function of the rate of dehydration: the more rapidly water can be lost, the less time is available for metabolism-linked damage, and the lower the water content that can be attained without lethal injury. However, recalcitrant seeds cannot lose structure-associated (non-freezable) water without sustaining lethal injury, which is considered as desiccation damage sensu stricto. Finally, the limited potential for storage of recalcitrant seeds is discussed, and the alternative biotechnological approach of germplasm conservation by means of cryostorage of embryonic axes, is presented.
South African Journal of Botany 67 (2) 2001, 90–149
©2001 NISC Pty Ltd, www.nisc.co.za
A taxonomic revision of Rafnia (Fabaceae, Crotalarieae)
GJ Campbell* and B-E van Wyk
Department of Botany, Rand Afrikaans University, PO Box 524, Auckland Park 2006, South Africa
* Corresponding author, e-mail: [email protected]
Received 31 May 1999, accepted in revised form 22 March 2000
Rafnia Thunb. is a relatively poorly known papilionaceous genus of the tribe Crotalarieae, and is endemic to the fynbos region of the Western and Eastern Cape Provinces of South Africa, with one species extending into KwaZulu-Natal. Characters of the habit, leaves, inflorescences, flowers, pods and seeds are useful for distinguishing among the 19 species, and variations in morphological characters are discussed. A cladistic analysis of 26 characters produced a cladogram with two distinct groups, which form the basis of the division of Rafnia into two sections (described in the taxonomic part of the paper). Five new species, namely R. rostrata G.J. Campbell & B-E. van Wyk, R. vlokii G.J. Campbell & B-E. van Wyk, R. alata G.J. Campbell & B-E. van Wyk, R. inaequalis G.J. Campbell & B-E. van Wyk and R. globosa G.J. Campbell & B-E. van Wyk are described. Four species are divided into subspecies, seven of which are described for the first time. The nomenclature, synonymy and typification of the 31 taxa are presented, as are descriptions, illustrations and distribution maps.
South African Journal of Botany 67 (2) 2001, 150–156
©2001 NISC Pty Ltd, www.nisc.co.za
The impact of alien plant invasion on mycorrhizas in mountain fynbos vegetation
N Allsopp1* and PM Holmes2
1 ARC-Range and Forage Institute, c/o Department of Botany, University of the Western Cape, Bag X17, Bellville 7535, South Africa
2 23 Dreyersdal Road, Bergvliet 7945, South Africa
* Corresponding author, e-mail: [email protected]
Received 14 November 1999, accepted in revised form 20 April 2000
We examined the effect of dense alien plant invasion on vegetation development following clearing, from a nutrient-acquisition perspective. The majority of fynbos plants form arbuscular mycorrhizas but Hakea and Pinus, two of the most invasive alien plant genera in mountain fynbos, do not. We hypothesised that these aliens would negatively impact on arbuscular mycorrhizal infectivity and thereby influence post-clearing vegetation development. The mycorrhizal status of vegetation at two mountain fynbos sites was compared between invaded and uninvaded sites before clearing and after alien clearing and fire. On cleared sites, non-mycorrhizal guilds were under-represented and arbuscular mycorrhizal guilds were over-represented. Soil arbuscular mycorrhizal infectivity and spore numbers were not affected by alien plants, possibly because an understorey of arbuscular mycorrhizal species had persisted in the alien stands. We conclude that following a single cycle of dense alien vegetation, arbuscular mycorrhizal plant species are not negatively affected and that other effects of alien vegetation on the environment are responsible for changes in plant guilds. Soil under alien plants was enriched and this may have contributed to the success of the arbuscular mycorrhizal guild after clearing.
South African Journal of Botany 67 (2) 2001, 157–160
©2001 NISC Pty Ltd, www.nisc.co.za
Isolation of Aureobasidium pullulans from Zimbabwean sources and glucosidase activities of selected isolates
RN Okagbue*, E Mwenje, T Kudanga, M Siwela and T Sibanda
Department of Applied Biology and Biochemistry, National University of Science and Technology, PO Box AC 939, Ascot, Bulawayo, Zimbabwe
* Corresponding author, e-mail: [email protected]
Received 1 September 1999, accepted in revised form 26 April 2000
The yeast-like fungus Aureobasidium pullulans (DeBary) Arnaud has been isolated and identified for the first time in Zimbabwe from diverse sources including fruits, leaves and commercial manure. Selective enrichment of an appropriate substrate using a minimal salts broth with shaking for two days at 25ºC followed by plating on a corresponding solid medium, proved to be a reliable method for isolating the fungus. Extracellular · and ß-glucosidases produced in both cultures by selected isolates were generally low; yields ranged from 0.7–1.4 units/mI and 1.7–2.5 units/mI respectively. Of six (mainly complex) nitrogen sources, NaNO3 supported the highest level of extracellular ·-glucosidase in A. pullulans Mn-2 despite a very low final pH (2.42). However, addition of Tween 80 to a 24 hour old culture led to a three-fold increase in yield of extracellular ·-glucosidase (approx. 6.0U/mI).
South African Journal of Botany 67 (2) 2001, 161–168
©2001 NISC Pty Ltd, www.nisc.co.za
Reconsideration of the status of Lavrania, Larryleachia and Notechidnopsis (Asclepiadoideae-Ceropegieae)
U Meve* and S Liede
Department of Plant Systematics, University of Bayreuth, D-95440 Bayreuth, Germany
* Corresponding author, e-mail: [email protected]
Received 11 January 2000, accepted in revised form 11 May 2000
Based on morphological, karyological and DNA sequence data the circumscription of Lavrania Plowes, Larryleachia Plowes and Notechidnopsis Lavranos and Bleck is reconsidered. The data presented point to an intermediate position of Notechidnopsis between the more distantly related Larryleachia and Lavrania. Keeping the three genera distinct is the best reflection of the complex relationships within this group.
South African Journal of Botany 67 (2) 2001, 169–176
©2001 NISC Pty Ltd, www.nisc.co.za
Photosynthesis and water relations of six tall genotypes of Cocos nucifera in wet and dry seasons
CHBA Prado1*, EEM Passos2 and JAPV de Moraes1
1 Universidade Federal de São Carlos, Departamento de Botânica, São Carlos, SP, Brazil, 13565-905
2 EMBRAPA-CPATC, Av. Beira Mar 3250, Aracaju, SE, Brazil, 49025-040
* Corresponding author, e-mail: [email protected]
Received 30 September 1999, accepted in revised form 19 May 2000
Despite the larger total amount of photosynthetic photon flux density (PPFD) in dry seasons, the integrated values of stomatal conductance (Gs), photosynthesis (A) and transpiration (E) were higher during the wet season in six tall genotypes of Cocos nucifera L. Average values of A and E from all genotypes were correlated with PPFD (r2 = 0.711, p <0.001) but not with Gs (r2 = 0.301) in the wet season. Conversely, A and E were strongly correlated with Gs (r2 = 0.776, p <0.001) but not with PPFD (r2 = 0.169) in the dry season. Five genotypes showed strong reduction (between 46–86%) of the integrated values of A, E and Gs in the dry season. Contrastingly, the Brazilian tall genotype (BRT) reduced only between 12–29% of the integrated values of leaf gas exchange in the dry season, tolerating lower values of leaf water potential and showing drought tolerance behavior more clearly. The integrated intrinsic water use efficiency increased up to 126% in the dry season in five genotypes but in BRT only 12%. Hence, the dry season imposed serious restrictions to water and carbon balances during the daily course. Such balances were sharply conditioned by an ambient variable (PPFD) in the wet season but by a biological controlled variable (Gs) in the dry season.
South African Journal of Botany 67 (2) 2001, 177–182
©2001 NISC Pty Ltd, www.nisc.co.za
A preliminary survey of plants used in traditional medicine in the Grahamstown area
B Matsiliza* and NP Barker
Department of Botany, Rhodes University, PO Box 94, Grahamstown 6140, South Africa
* Corresponding author, e-mail: [email protected]
Received 1 November 1999, accepted in revised form 20 May 2000
On the basis of interviews with traditional healers, diviners and villagers in the Grahamstown area, twenty-four plants used in traditional medicine are reported. The preparation and utilisation of these plants is as varied as the plants themselves. Some of the plants were previously known to ethnobotanists but because of the diversity of tribal groups in South Africa, new preparations of these plants were discovered. This also suggests that there are gaps in recorded knowledge of medicin