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2.8.4.2 Potassium nitrate Literature review This chemical is commonly used to encourage seed germination, with solutions of 0.1 and 1.0% frequently being used in germination tests (COPELAND, 1976). KNO3 has been shown to act synergistically with factors such as temperature and media supplementation with kinetin and gibberellic acid. Seeds sensitive to KNO3 are often also sensitive to light (COPELAND, 1976). 2.8.4.3 Ethylene Increased ethylene evolution accompanies seed germination of many species (BASKIN & BASKIN, 1998). Ethylene promotes its own biosynthesis during pea seed germination by positive feedback regulation of 1-aminocyclopropane-1-carboxylic acid oxidase. 2.8.4.4 Smoke Many plant species have shown increased percentage germination and vigour after exposure of seeds or seedlings to smoke water (MINORSKY, 2002). These include plants naturally adapted to areas of high fire frequency as well as some species that are not specifically adapted to these conditions. These include agriculturally useful species, such as maize (SPARG et al., 2006) and lettuce (BROWN & VAN STADEN, 1997), as well as many aesthetically useful species, such as those naturally occurring in fynbos (BROWN & VAN STADEN, 1997). Species originating from natural fire-prone habitats include many species of South African fynbos such as the fire-climax grass, Themeda triandra (Poaceae) and members of the Mesembryanthemaceae (BROWN & VAN STADEN, 1997). Other examples of such smoke water stimulated plants include species of the California chaparral and many other fire-prone communities (BLANK & YOUNG, 1998). It has been suggested that the promotive effect of smoke is independent of seed size and shape, plant life form and fire sensitivity (BROWN & VAN STADEN, 1997). Smoke can also be utilised as an effective seed pre-sowing treatment, as the stimulatory effect of smoke is irreversible and cannot be leached (LIGHT et al., 2002). Seeds treated with smoke are known to retain this stimulatory effect even after a year of storage (MINORSKY, 2002). The inhibitory effects of high smoke concentrations appear to be reversible and seeds grow with increased vigour after the smoke has been leached to a 49
Literature review tolerable level (LIGHT et al., 2002). This effect would be a favourable adaptation to a post-fire environment as the inhibitory compounds will only leach with sufficient rainfall (LIGHT et al., 2002). Smoke thus enables seeds to germinate at the right time, grow faster and have a more robust root system and so have a major competitive advantage in their natural environment (BLANK & YOUNG, 1998). In early experiments by DE LANGE and BOUCHER (1990), smoke was generated by burning a mixture of fresh and dry plant material in a metal drum. This smoke was then fed into a polythene tent and allowed to settle on the soil where the seeds were stimulated to germinate. One disadvantage is that the germination cue of smoke is easily confused with the effect of temperature on germination. This is because temperatures slightly higher than ambient temperature significantly increase seedling emergence in many species (BASKIN & BASKIN, 1998). Due to the complications of separating smoke from high temperatures, direct exposure to smoke is not recommended. Aqueous smoke extracts were pioneered by DE LANGE and BOUCHER in 1990 and since then many authors have demonstrated that the active component of airborne smoke is soluble in water (BROWN & VAN STADEN, 1997; TAYLOR & VAN STADEN, 1998; SPARG et al., 2005). The method for preparing such a solution usually involves forcing smoke that has been generated in a drum to bubble through water (BROWN & VAN STADEN, 1997). Combustion usually proceeds slowly and the burning material is made to smoulder, thus releasing relatively large quantities of smoke (BROWN & VAN STADEN, 1997). In an experiment conducted by JÄGER et al. (1996) it was found that aqueous smoke extracts prepared from a range of plants, as well as extracts prepared by heating agar and cellulose contained compounds which stimulated the germination of Grand Rapids lettuce seed. They also demonstrated that the same active compound is produced by burning Themeda triandra leaves, agar and cellulose by providing evidence obtained by thin-layer chromatography and high-performance liquid chromatography. This was also demonstrated with the same methods by BROWN and VAN STADEN (1997). 50
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Propagation of Romulea species Pier
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Contents 2.7 GERMINATION PHYSIOLOGY
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Contents 5.3.1 Explants from seedli
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Abstract The suitability of various
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Declarations I Pierre André Swart,
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Declarations DETAILS OF CONTRIBUTIO
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Publications from this thesis ASCOU
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List of Figures Figure 2.13: Suther
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was significantly different from th
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List of Tables Table 2.1: Names of
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List of Abbreviations 2,4-D 2,4-Dic
Page 23 and 24: Die vlakhaas spits sy oor hy het di
Page 25 and 26: As die mens dan ook so sy dankbaarh
Page 27 and 28: Introduction where a great number o
Page 29 and 30: Introduction The subgenera Romulea
Page 31 and 32: 2 Literature review Leef van daad e
Page 33 and 34: Literature review Figure 2.2: Life
Page 35 and 36: Literature review Figure 2.4: Life
Page 37 and 38: Literature review The plants are sh
Page 39 and 40: Literature review flowers (DE VOS,
Page 41 and 42: Literature review often found on cl
Page 43 and 44: Literature review flowers of R. lei
Page 45 and 46: Literature review flattened upper s
Page 47 and 48: 2.2.16 Romulea tabularis Literature
Page 49 and 50: Literature review extinct, R. papyr
Page 51 and 52: Literature review R. leipoldtii occ
Page 53 and 54: Literature review Figure 2.8: Calvi
Page 55 and 56: Literature review Figure 2.14: Fras
Page 57 and 58: Figure 2.20: Nieuwoudtville weather
Page 59 and 60: Literature review Figure 2.26: Grah
Page 61 and 62: Literature review Figure 2.29: Diag
Page 63 and 64: Literature review Figure 2.30: A te
Page 65 and 66: Literature review Macronutrients ca
Page 67 and 68: Literature review The soils of the
Page 69 and 70: Literature review The embryo is the
Page 71 and 72: Literature review Phase 2 is seen a
Page 73: Literature review endogenous gibber
Page 77 and 78: Literature review these channels pe
Page 79 and 80: Literature review 2.8.7 Seed dorman
Page 81 and 82: Literature review the embryo (COPEL
Page 83 and 84: Literature review germinated under
Page 85 and 86: Literature review (COPELAND, 1976).
Page 87 and 88: 2.9 BRIEF REVIEW OF IN VITRO CULTUR
Page 89 and 90: Literature review (DEBERGH, 1994).
Page 91 and 92: Literature review PIERIK (1997) sta
Page 93 and 94: Literature review The distinguishin
Page 95 and 96: Literature review The essential fun
Page 97 and 98: 2.9.3.4 Abscisic acid Literature re
Page 99 and 100: Table 2.6: Example of a matrix to e
Page 101 and 102: Literature review Young embryos req
Page 103 and 104: Literature review and the addition
Page 105 and 106: Literature review organ is then pro
Page 107 and 108: Literature review environmental str
Page 109 and 110: 2.11 IN VITRO FLOWERING Literature
Page 111 and 112: Literature review higher regenerati
Page 113 and 114: Subfamily Ixioideae (continued) Tri
Page 115 and 116: Literature review Table 2.8: Corm i
Page 117 and 118: 3 Investigation into the habitat of
Page 119 and 120: Soil sampling and analysis The firs
Page 121 and 122: Soil sampling and analysis Table 3.
Page 123 and 124: 4 Germination physiology 4.1 INTROD
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4.2.2 Water content and imbibition
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Germination physiology (-N), phosph
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Germination physiology rosea seeds
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Germination physiology Figure 4.4:
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Germination (%) 50 40 30 20 10 0 77
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Germination (%) 100 80 60 40 20 0 c
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Germination physiology The relative
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Germination physiology seeds of R.
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5.2 MATERIALS AND METHODS In vitro
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In vitro culture initiation and mul
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5.2.3 Explant comparison In vitro c
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5.4 DISCUSSION In vitro culture ini
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6 In vitro corm formation and flowe
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In vitro corm formation and floweri
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6.3 RESULTS 6.3.1 Corm formation In
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Commercialization potential of Romu
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Commercialization potential of Romu
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BASKIN, C. C., and BASKIN, J. M. (1
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Literature cited DOWLING, P. M., CL
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Literature cited HILTON-TAYLOR, C.
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Literature cited KUMAR, A., SOOD, A
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Literature cited PIERIK, R. L. M. (
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Literature cited STEINITZ, B., COHE
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