Smoke Seed Germination Studies and a Guide to Seed Propagation of Plants from the Major Families of the Cape Floristic Region, South Africa
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View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Elsevier - Publisher Connector South African Journal of Botany 2004, 70(4): 559–581 Copyright © NISC Pty Ltd Printed in South Africa — All rights reserved SOUTH AFRICAN JOURNAL OF BOTANY ISSN 0254–6299 Smoke seed germination studies and a guide to seed propagation of plants from the major families of the Cape Floristic Region, South Africa NAC Brown* and PA Botha1 Horticultural Research, Conservation and Ecology, Kirstenbosch Research Centre, South African National Biodiversity Institute, Private Bag X7, Claremont 7735, Cape Town, South Africa 1 Present address: Millennium Seed Bank Project, Royal Botanic Gardens Kew, Wakehurst Place, United Kingdom * Corresponding author, e-mail: [email protected] Received 8 April 2004, accepted in revised form 21 April 2004 Fynbos is the dominant vegetation of the Cape Floristic in the wild and these cues have to be simulated when Region (CFR), one of world’s richest regions in terms of attempting to germinate wildflower seed in the laborato- its biodiversity and a region in which over two-thirds of ry and nursery. This study reports on the germination the plant species and seven of the plant families are response to smoke of 283 species from 39 families of endemics. Many fynbos species from the major families fynbos. In addition seeds of some of the species were such as the Proteaceae, Ericaceae, Asteraceae and subjected to other dormancy breaking treatments and Restionaceae are cultivated as ornamentals or are of these results, together with results of similar treatments importance as floricultural crops. Propagation of fynbos reported in the literature, are included. Results from plants from seed is often difficult, as seeds of many these germination trials have been used to provide new species are dormant when shed and require very spe- general guidelines or protocols for germinating fynbos cific environmental ‘messages’ or cues before they will seeds in the nursery or to update the previously pub- germinate. Fire provides the major cues for germination lished ones. Introduction The Cape Floristic Region (CFR) covers an area of 90 000km2 mer drought, low soil fertility and periodic fires. The fires (35 000 sq miles) in the south western Cape, at the southern have a frequency of 4–40 years and are a natural phenom- tip of Africa. This is less than four percent of the area of South enon in fynbos (Kruger 1983). Seeds of many wildflowers Africa, yet it contains 9 000 plant species. It is one of world’s are adapted to germinate in response to one or more of the richest regions in terms of its biodiversity and over two-thirds cues provided by fire. Heat from flames may fracture the of the plant species and seven of the plant families are impermeable seed coat of hard-seeded species (e.g. endemics (Goldblatt and Manning 2000a). Fynbos is the Fabaceae) resulting in the coats becoming permeable to unique type of vegetation that is dominant in the CFR. It is a water. Dry heat may also break dormancy by providing a community of small shrubs, evergreen and herbaceous heat-pulse that stimulates the embryo directly and results in plants and bulbs and is exceptionally rich in species. It is per- germination (e.g. Restionaceae). Dry heat has also been haps best known as the home of the South African Proteas reported to break seed dormancy of some South African (sugarbushes, pincushions and conebushes), Ericas (Cape Leucospermums (pincushions, family Proteaceae) by com- heaths) and Helichrysums (everlastings), and is also typified plete desiccation of their oxygen-impermeable seed coats. by the Restionaceae (Cape reeds or Cape grasses) (Brown When rain falls the dry coats, which are permeable to water, et al. 1995, Goldblatt and Manning 2000a). split suddenly and the embryo then obtains sufficient oxygen Many of the wildflowers from these families are cultivated for germination. Fires also provide chemical messages or as ornamentals in parks and gardens around the world or cues, such as the gases of ethylene and ammonia, which are of importance as floricultural crops. Propagation of fyn- stimulate germination in some species of Erica. In addition bos plants from seed is often difficult, as seeds of many to the more obvious cues provided by heat, it was discov- species are dormant when shed and require very specific ered by De Lange and Boucher (1990) that smoke from fyn- environmental ‘messages’ or cues before they will germinate bos fires provides a major chemical cue that is responsible (Brown 1993a). The fynbos occurs in areas with a for stimulating the germination of seed of many fynbos Mediterranean climate (winter rainfall) and the environment species. The chemical cue has recently been identified by is characterised by a number of stress factors such as sum- Flematti et al. (2004) and Van Staden et al. (2004). To date, 560 Brown and Botha 283 species from 39 families have been tested and 161 of Germination data from plant growth regulator trials these have given a positive response. Amongst those responding are the horticulturally important species of the For selected species, germination data was recorded from Cape Reeds (Restionaceae), Everlastings (Asteraceae) and experiments in which seeds were soaked in solutions of indi- Brunias (Bruniaceae), (Brown 1993b, Van Staden et al. vidual growth regulators for 24h. Seeds were then removed 1995). Fire may also have an indirect effect on germination from the solutions and incubated under the same conditions by causing changes in the soil temperature regimes in the as the smoke treated seeds. (Brown 1993a, Brown et al. immediate post-fire environment (Brown 1993a). Fire thus 1993). Data from previously published trials by Brits (1986a, provides the major cues for germination in the wild and 1996), Brown and Drewes (1991), Small et al. (1982) and these cues have to be simulated when attempting to germi- Van de Venter and Esterhuizen (1988) using growth regula- nate wildflower seed in the laboratory and nursery. tors and other chemicals to break dormancy of fynbos seeds In a study of the effect of smoke in breaking dormancy one are included in tables of results. cannot ignore the fact that a smoke requirement for germi- nation may be one of a number of factors (internal and exter- Germination data from heat and scarification trials nal) imposing dormancy. For example, in situations where dormancy is partly coat-imposed, smoke stimulation may For selected species, germination data was recorded from only occur once the coat is treated in some way to allow full experiments in which seeds were either scarified lightly uptake of water and oxygen and unhindered expansion of between two sheets of sandpaper or heated in an oven at the embryo, (whichever process has been hindered by the 100°C for 10min, or placed in hot water at 100°C and then intact seed coat). In the laboratory and plant nursery the the water was allowed to cool. Seeds were then incubated known plant growth regulators (gibberellins, cytokinins and under the same conditions as the smoke treated seeds. ethylene) are frequently applied to seeds to relieve embryo (Brown 1993a, Brown et al. 1993). Data from previously dormancy. Each may break embryo dormancy on its own or published heat trials on species of Restionaceae (Musil and in combination with one or more other regulators. There is De Witt 1981) and species of Erica (Van de Venter and also the possibility that they may interact and have a syner- Esterhuizen 1988) are included in the tables of results. gistic effect with smoke (Thomas and Van Staden 1995). The major emphasis of this study has been on studying Format for presentation of germination results the germination response of fynbos species to smoke. The framework for the presentation of results has been the Where available, actual germination results for dormancy degree of response to smoke, ranging from the very marked breaking treatments and for controls are given in tables. In response of 1 000% or more increase in germination to a nil addition, figures for germination have been converted to a response. For selected species the effect of heat, scarifica- percentage improvement in response over the results for the tion and growth regulators and their interaction with smoke water control treatments. For smoke treatments, these per- has also been studied. This smoke and other germination centage responses were divided further into the following data is summarised for each family studied and protocols groups: percentage response greater than 1 000% and per- have been drawn up as a guide to follow to obtain optimum centage response less than 1 000%. Where responses, but germination for species in each family. no actual germination percentages, are given in published texts, the abbreviation NGPG is used in tables. Materials and Methods Results and Discussion Collation of smoke germination data Seed propagation protocols for some of the families of Germination data presented in this study consist of new and horticultural importance unpublished data recently generated in laboratory and nurs- ery trials, together with smoke germination data from previ- Based on the germination results obtained in the smoke, ously published studies. Seeds used in the current study plant growth regulator, heat and scarification trials, response where collected from natural populations in the wild in vari- groups of species, responding in a particular way, were iden- ous localities in the south western and southern Cape tified in each family. Protocols for germinating seed were Province from a minimum of 100 (on average, 200–300) worked out for each response group. These protocols are for individual plants per species representative of the popula- use as a general guide to the procedures to be followed for tion.