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Download The SEED GERMINATION CHARACTERISTICS OF •CENTAUREA DIFFUSA AND C. MACULOSA By DARYL GUY NOLAN B.Sc, The University of British Columbia, 1984 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES (Department of Plant Science) We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA November 1989 ©Daryl Guy Nolan, 1989 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department The University of British Columbia Vancouver, Canada Date October m DE-6 (2/88) ii ABSTRACT The problematic reinfestation of chemically-treated sites by diffuse and spotted knapweed {Centaurea diffusa and C. maculosa) is thought to occur from dormant seeds in the soil. This study confirmed that reserves of dormant seeds are present in the soil of infested sites, although greater numbers of seeds were recovered from senesced plants. Knapweed plants produce both non-dormant and dormant seeds (germination polymorphism), the relative proportions of which vary between individual plants within a site, as well as between bulk samples collected from different sites. Two types of dormant seeds were identified. Dormancy of some seeds was broken by exposure to red light ('light-sensitive seeds'). Light- sensitivity was evident at 10, 15, 20, 25, and 30 °C. Germination in light-sensitive seeds was shown to be mediated by phytochrome. A lesser number of dormant seeds failed to respond to red light ('light-insensitive seeds'). Dry after-ripening released dormancy in both light-sensitive and light-insensitive seeds. However, no apparent loss of dormancy from after-ripening occurred when the relative humidity was too low or too high. At the highest relative humidity level tested (90.7%), dormancy was induced in some seeds while other seeds died. Dormancy was also induced when imbibed seeds were incubated in darkness at 25, 30, 35, and 40 °C for 5 days. Dormancy induction was greatly enhanced by incubating submerged seeds in de-oxygenated water (anaerobiosis). However, some seeds died when incubated anaerobically for 5 days. Dormancy was broken in a small percentage of dormant seeds by incubation in a 10 mM solution of potassium nitrate or potassium nitrite; 100 mM potassium nitrite killed most seeds. Gibberellic acid was a much stronger germination stimulant. Some dormant seeds germinated at 25 °C if they were previously chilled at 3 °C. To compare laboratory findings with field germination behaviour, seeds from two samples of each species were buried to a depth of about 3 cm in mesh packets during November, April and August near Salmon Arm, B. C. Seeds exhibiting higher levels of germination in darkness in vitro also germinated to higher levels in situ when burial occurred iii in November. However, burial in April and August led to lower germination levels in situ. Light sensitivity was still prominent following 17 months of burial. Most of the decline in viable seed numbers during burial were attributable to in situ germination. Theoretical discussions of the source of germination polymorphism in knapweed seeds, the importance of light to field germination and seedling mortality, and a potential strategy for controlling these weeds are presented. iv TABLE OF CONTENTS ABSTRACT ii LIST OF TABLES viii LIST OF FIGURES xi ACKNOWLEDGMENT xiii 1.0 INTRODUCTION 1 2.0 LITERATURE REVIEW OF KNAPWEED BIOLOGY AND CONTROL 2.1 Detrimental Consequences of Knapweed Invasion 2.1.1 Forage Production 2 2.1.2 Rangeland Management 3 2.1.3 Livestock Injury 3 2.1.4 Miscellaneous Effects 3 2.2 Geographic Distribution 2.2.1 Present Distribution 4 2.2.2 Potential Distribution in Canada 4 2.3 Control 2.3.1 Chemical 5 2.3.2 Biological Control 6 2.3.3 Cultural 2.3.3.1 Exclusion 6 2.3.3.2 Range seeding 7 2.3.3.3 Burning 7 2.3.3.4 Cultivation 7 2.3.3.5 Mowing or grazing 8 2.3.3.6 Fertilization 8 2.3.3.7 Irrigation 9 2.4 Knapweed Biology 2.4.1 Taxonomy 9 2.4.2 Favoured Habitat 11 2.4.3 Life Cycle 2.4.3.1 Life span 12 2.4.3.2 Germination 14 2.4.3.3 Seedlings 16 2.4.3.4 Rosettes 16 2.4.3.5 Bolted plants 20 2.4.3.6 Flower production 22 2.4.3.7 Seed production 22 2.4.3.8 Seed dispersal 25 2.4.3.9 Seed bank 28 2.5 Knapweed Seed Physiology 28 V 3.0 EFFECT OF LIGHT ON KNAPWEED SEED GERMINATION 3.1 Background 3.1.1 Light Sensitive Germination in the Asteraceae 30 3.1.2 Properties of Phytochrome 30 3.1.3 Phytochrome Mediation of Field Germination 34 3.1.4 Objectives 36 3.2 Materials and Methods 3.2.1 Seed Collection and Storage 37 3.2.2 Incubation Conditions 37 3.2.3 Light Sources 39 3.2.4 Germination Behaviour of Seeds From Different Sites and Clutches ..39 3.2.5 Reversibility of R and FR Effects on Germination 41 3.2.6 Effect of R Duration on Germination 42 3.2.7 Statistical Procedures 42 3.3 Results 3.3.1 Seeds from Different Sites and Clutches 42 3.3.2 Effect of Sequential R and FR Light Exposures 46 3.3.3 Effect of Duration of R 46 3.4 Discussion 48 4.0 EFFECT OF LIGHT QUALITY DURING SEED MATURATION 4.1 Background 54 4.2 Materials and Methods 57 4.3 Results and Discussion 58 5.0 EFFECT OF AFTER-RIPENING ON GERMINATION BEHAVIOUR 5.1 Background 61 5.2 Materials and Methods 5.2.1 Effect of Aging on Germination Behaviour 61 5.2.2 Effect of Relative Humidity on After-Ripening 63 5.3 Results 5.3.1 Effect of Aging on Germination Behaviour 5.3.1.1 Level of ND seeds 63 5.3.1.2 Level of LI seeds 65 5.3.1.3 Level of IR seeds 71 5.3.2 Effect of Relative Humidity on After-Ripening 5.3.2.1 ND seed levels 71 5.3.2.2 IR seed levels 79 5.3.2.3 LI seed levels 79 5.4 Discussion 5.4.1 Conformity of Results with Previous Reports 79 5.4.2 Proposed Model of Dormancy Transition in Dry Knapweed Seeds 85 5.4.3 After-Ripening: A Source of Germination Polymorphism in Diffuse and Spotted Knapweed? 86 5.4.4 Regulation of Field Germination 88 5.4.5 After-Ripening: Considerations in Seed Germination Behaviour Studies 88 vi 6.0 EFFECT OF TEMPERATURE ON IMBIBED KNAPWEED SEEDS 91 6.1 Constant Temperature 6.1.1 Background 92 6.1.2 Materials and Methods 92 6.1.3 Results 6.1.3.1 Dark germination 93 6.1.3.2 Light sensitivity 93 6.1.3.3 Seed viability 93 6.1.4 Discussion 96 6.2 Effect of Temperature During Dark Incubation on Subsequent Germination Behaviour at 25 °C 98 6.2.1 Materials and Methods 98 6.2.2 Results 6.2.2.1 Dark germination 99 6.2.2.2 Germination following exposure to 2 min R 102 6.2.2.3 Germination following 1 d R exposure 103 6.2.2.4 Discussion 103 6.3 Effect of Chilling Duration on Seed Germination 105 6.3.1 Materials and Methods 106 6.3.2 Results 6.3.2.1 Transfer to 20 °C .....106 6.3.2.2 Transfer to 25 °C 108 6.3.3 Discussion 108 7.0 EFFECT OF ANAEROBIOSIS ON SECONDARY DORMANCY INDUCTION 7.1 Background 113 7.2 Materials and Methods 113 7.3 Results 7.3.1 Dark Germination 114 7.3.2 Seed Viability 114 7.3.3 Germination Following 2 min R 119 7.3.4 Germination Following ldR 119 7.4 Discussion 124 8.0 EFFECT OF NITRATE AND NITRITE ON GERMINATION 8.1 Background 126 8.2 Materials and Methods 8.2.1 Effect of Nitrate on Germination 8.2.1.1 Effect of nitrate concentration and temperature on dark germination 126 8.2.1.2 Effect of light and nitrate 127 8.2.2 Effect of Nitrite 8.2.2.1 Preliminary screening of effect on dark germination 127 8.2.2.2 Effect of nitrite and light 127 8.3 Results 8.3.1 Nitrate 8.3.1.1 Dark germination 128 8.3.1.2 Effect of nitrate and R at 20 °C 128 8.3.2 Nitrite 8.3.2.1 Dark germination 133 8.3.2.2 Nitrite and R treatment 133 8.4 Discussion 133 vii 9.0 EFFECT OF GIBBERELLIC ACID ON KNAPWEED SEED GERMINATION 9.1 Background 139 9.2 Materials and Methods 9.2.1 Germination Dose Response to Exogenous GAg 139 9.2.2 GAg, Light, and Seed Coat Excision 139 9.3 Results 9.3.1 Germination Dose Response 141 9.3.2 GAg, Light, and Seed Coat Excision 141 9.4 Discussion 144 10.0 SEED PERSISTENCE IN THE SOIL AND ON SENESCED PLANTS 10.1 Background 145 10.2 Numbers of Soil-borne Knapweed Seeds 10.2.1 Materials and Methods 146 10.2.2 Results 147 10.3 Numbers of Seeds Retained on Senescent Plants 10.3.1 Materials and Methods 150 10.3.2 Results 151 10.3.3 Discussion 153 10.4 Effect of Burial on the Germination Characteristics of Knapweed Seeds 10.4.1 Materials and Methods 155 10.4.2 Results and Discussion 156 11.0 A THEORETICAL EXPLANATION FOR KNAPWEED DISTRIBUTION AND ITS POSSIBLE MANAGERIAL IMPLICATIONS 170 12.0 CONCLUSIONS 179 13.0 BIBLIOGRAPHY 181 14.0 APPENDIX 201 viii LIST OF TABLES Table Page 1 Knapweed Distribution in Western North America 4 2 Seed Collection Sites (British Columbia) 38 3 Germination of Diffuse Knapweed Seeds Collected From Different Sites 43 4 Germination of Spotted Knapweed Seeds Collected From Different Sites 44 5 Comparative Germination of Different Knapweed Seed Clutches Within Sites 45 6 Reversibility of R and FR Effects on Knapweed Seed Germination 47 7 Mean Germination of Seeds Matured in Capitula Surrounded by Various Light Filters 59 8 Effect of After-ripening at 25 °C on Percentage of ND Seeds 64 9 Effect of After-ripening at 3 °C on Percentage of ND Seeds 66 10 Effect of After-ripening at -20 °C on Percentage of ND Seeds
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