AN ABSTRACT OF THE THESIS OF Jean Ann Gleichsner for the degree of Doctor of Philosophy inCrop Sciencepresented on June 27, 1988 . Title: Biology of Bromus rigidus: Interference in Winter Wheat, Seed Longevity in the Soil, and Vernalization Requirements for Flowering Abstract approved:!Redacted for Privacy / 1 Arnold P. Appleby Greenhouse and field studies were conducted to examine various biological aspects of ripgut brome (Bromus rigidus Roth). A field experiment was conducted to measure the grain yield of winter wheat (Triticum aestivum L. Stephens') at various ripgut brome and wheat plant densities. Wheat yield decreased as ripgut brome density increased at all wheat seeding rates (56, 112, 168, and 224 kg/ha). Grain yield was unaffected by wheat seeding rate in the absence of brome. Increasing seeding rates above 112 kg/ha to reduce wheat yield loss caused by ripgut brome is ineffective. In the field, both surface-sown and buried (1 to 30 cm) ripgut brome seed were depleted within 15 months. Persistence of surface-sown seed declined slowly during the first year, falling from 83 to 62 to 23% after 1, 9, and 12 months, respectively. Seed covered by soil, however, germinated more rapidly, with less than 10% of the initial population ungerminated after 1 month at all depths. The mode of seed disappearance was closely related to whether or not seed were covered with soil. Seed loss at depths of 1 to 30 cm was primarily due to germination in situ, with little effect from viability loss or enforced or induced dormancy. In contrast, the persistence of surface-sown seed was due primarily to induced dormancy for up to 12months, with nonviability loss and enforced dormancy becoming important thereafter. Ripgut brome has a quantitative requirement for vernalization in order to flower. In greenhouse studies, cold treatment (5 + 2 C) of 2, 4, or 6 weeks shortened the vegetative period, but longer exposure did not further decrease the time required to flower. Plants vernalized as imbibed seed for 8 weeks took 17 days to flower following transfer from cold treatment to the greenhouse. Unvernalized controls flowered 53 days after planting in the greenhouse. Highest total seed dry weight and total shoot dry matter was produced by unvernalized plants; lengthening periods of vernalization from 2 to 8 weeks decreased both measurements. In field studies, ripgut brome plants established in the fall flowered sooner after resumption of growth in the spring than those planted in the spring. Plants seeded after April failed to flower until the following spring. Biology of Bromus rigidus: Interference in Winter Wheat, Seed Longevity in the Soil, and Vernalization Requirements for Flowering by Jean Ann Gleichsner A THESIS submitted to Oregon State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy Completed June 27, 1988 Commencement June 1989 APPROVED: Redacted for Privacy Professor of Crop Science in /clerge of jor Redacted for Privacy Head of Department, Crop Science Redacted for Privacy Dean of Graduate School Date thesis presented June 27, 1988 Typed by Jean A. Gleichsner ACKNOWLEDGEMENTS I consider myself extremely fortunate to have made some very good friends while studying at Oregon State University. Two friends that deserve special mention are Bernal Valverde and Dan Peek. This thesis would not have been possible without their help and encouragement. Despite many trying moments, they refused to give up on me and more importantly made sure I didn't give up. Their tactics weren't always pleasant, but they were sure effective. I also would like to extend gratitude to their families for providing friendship and some very memorable moments. I am very grateful to Bob Spinney and Bill Brewster for their help in getting my field work done. Even with their demanding workload, they always made time to help me.Many thanks to Jeannette Emry for her secretarial assistance. I thank the members of my graduate committee, Dr. Arnold Appleby, Prof. Larry Burrill, Dr. Mark Wilson, Dr. Kenton Chambers, and Dr. Tom Bedell for their time and guidance. I also am grateful to Dr. Roger Fendall for the opportunity to teach the Crop Science Laboratory.Teaching and interacting with students were some of the brightest moments at Oregon State. Special thanks to my parents and family. Although they didn't always understand what I was doing, they were always there to provide love and support. Thank you Mom for encouraging my dream of teaching. Looks like I finally made it come true. Jane, its difficult to express my appreciation for the financial support you gave me throughout my college years. You really don't know how important it was to me. Bonnie, thank you for keeping me up with the news on the home front. Even though I couldn't be there, you made sure I knew what was going on. Finally, a sincere thank you to Caren Augustine. Despite the distance and lack of contact, you have remained a very good and dear friend to me. TABLE OF CONTENTS INTRODUCTION 1 CHAPTER 1. Ripgut brome (Bromus rigidus) interference in winter wheat: Plant density effects. 7 Abstract 7 Introduction 8 Materials and Methods 9 Results and Discussion 11 Literature Cited 21 CHAPTER 2. Effect of depth and duration of seed burial on ripgut brome (Bromus rigidus). 22 Abstract 22 Introduction 23 Materials and Methods 25 Results and Discussion 29 Literature Cited 40 CHAPTER 3. Vernalization requirements for flowering of ripgut brome (Bromus rigidus). 42 Abstract 42 Introduction 43 Materials and Methods 45 Results and Discussion 50 Literature Cited 59 GENERAL DISCUSSION 61 BIBLIOGRAPHY 66 APPENDIX 69 LIST OF FIGURES Figure Page 1.1 Effect of brome density on wheat grain yield 18 1.2 Effect of brome density on total wheat shoot 19 number per unit area. 1.3 Effect of brome density on wheat above-ground 20 biomass. 2.1 Monthly precipitation and mean monthly soil 38 temperature at a depth of 10 cm from November 1985 to October 1987 recorded at Hyslop Research Farm near Corvallis, Oregon. 2.2 Model used to partition weed seed recovered 39 from soil into components of persistence (Pex Pend) and depletion (Dg + Dn). 3.1 Effect of date of planting in the field on the 58 emergence and flowering of ripgut brome. LIST OF TABLES Table Page 1.1. Comparison of yield regression lines for 15 homogeneity of intercepts and slopes. 1.2. Average winter wheat grain yields attained 16 with varied winter wheat seeding rates and ripgut brome densities. 1.3. Effect of brome density and wheat seeding 17 rate on total brome shoot number per unit area. 2.1. Effect of depth and duration of burial on 33 persistence (Pex Pend) of ripgut brome seed. 2.2. Effect of depth and duration of burial on 34 in situ germination (Dg) of ripgut brOme seed. 2.3. Effect of depth and duration of burial on 35 nonviability loss (Dn) of ripgut brome seed. 2.4. Effect of depth and duration of burial on 36 enforced dormancy (Pex) of ripgut brome seed. 2.5. Effect of depth and duration of burial on 37 induced dormancy (Pend)of ripgut brome seed. 3.1. Mean daily maximum and minimum monthly air 54 temperature recorded at Hyslop Research Farm near Corvallis, Oregon. 3.2 Effect of vernalization duration at 5 C on days 55 to flowering, culms per plant, plant height, total seed dry weight, total shoot dry weight, and the ratio of seed dry weight to shoot dry weight of ripgut brome after transfer to the greenhouse. 3.3 Effect of outdoor cold treatment on days to 56 flowering, culms per plant, total seed dry weight, total shoot dry weight, and the ratio of seed dry weight to shoot dry weight of ripgut brome after transfer to the greenhouse. LIST OF APPENDIX TABLES Table Page 1. Effect of ripgut brome density on winter wheat 69 grain yield. 2. Analysis of variance table for effect of ripgut 70 brome density on winter wheat grain yield. 3. Effect of winter wheat seeding rate and ripgut 71 brome density on total number of winter wheat shoots per unit area. 4. Effect of ripgut brome density on total number 72 of ripgut brome shoots per unit area. 5. Effect of winter wheat seeding rateand ripgut 73 brome density on total winter wheatabove-ground biomass. 6. Effect of winter wheat seeding rateand ripgut 74 brome density on total ripgut bromeabove-ground biomass. 7. Effect of vernalization duration at 5 C on days 75 to flowering, culms per plant, total shoot dry weight, total seed dry weight, and ratio of seed dry weight to shoot dry weight of ripgut brome after transfer to the greenhouse. Year 1. 8. Effect of vernalization duration at 5 C on days 78 to flowering, culms per plant, total shoot dry weight, total seed dry weight, and ratio of seed dry weight to shoot dry weight of ripgut brome after transfer to the greenhouse. Year 2. 9. Analysis of variance table for effect of vernal- 81 ization duration at 5 C on days to flowering of ripgut brome after transfer to the greenhouse. 10. Analysis of variance table for effect of vernal- 81 ization duration at 5 C on culms per plant of ripgut brome after transfer to the greenhouse. 11. Analysis of variance table for effect of vernal- 82 ization duration at 5 C on total shoot dry weight of ripgut brome after transfer to the greenhouse. 12. Analysis of variance table for effect of vernal- 82 ization duration at 5 C on total seed dry weight of ripgut brome after transfer to the greenhouse.