REPRODUCTIVE BIOLOGY IN POA ANNUA L. A THESIS SUBMITTED TO THE FACULTY OF THE GRADUATE SCHOOL OF THE UNIVERSITY OF MINNESOTA by Bridget Anne Ruemmele IN PARTIAL FULLFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY 1989
copy right Bridget Anne Ruemmele 1989
ACKNOWLEDGEMENT My sincerest gratitude is extended to my advisors, Dr. Peter D. Ascher and Dr. Donald B. White, as well as the remainder of my Ph.D. advisory committee: Drs. James Luby, Robert Busch, David Biesboer, and Nancy Ehlke, for their constructive suggestions throughout my graduate school endeavors. I am indebted to my advisors' unselfish willingness to assist me on the completion of my degree in a timely manner. Another person to whom singular recognition is due is my friend and colleague, Charleen Baker. Her eternal optimism and enthusiasm were available whenever necessary, keeping me on course toward my degree. I also wish to express appreciation to my other colleagues, friends, and family for believing in my abilities and providing encouragement for the duration of this experience.
I would like to acknowledge the following Alexander P. Anderson and Lydia Anderson Fellowship from the University of Minnesota, 0. J. Noer Turf Grass Research Foundation, and United State Golf Association for the funding of this research.
THESIS ABSTRACT Bridget Ruemmele 348 words REPRODUCTIVE BIOLOGY.IN POA ANNUA L. Poa annua, often considered a weedy grass, comprises a major turf component on many golf courses in temperate regions. Potential for developing improved cultivars has been suggested by extensive variation, including stoloniferous and perennial growth habits, dark green and fine-textured leaves, good rooting ability, and tolerances to environmental stresses. Poa annua is usually reported as self compatible, with 2 to 15 percent outcrossing. To facilitate a breeding and selection program to improve this species for golf turf use, an analysis of reproductive biology of included germplasm was required. The objectives were to develop an acceptable method to isolate inflorescences used in analyses of reproductive biology of Poa annua and to determine selfing and outcrossing potentials in. Poa annua. Biotypes from sites in Canada, Europe, and the United States were studied using observations of morphology, anthesis, pollen tube development, aporoixis, and seed yield from self, sib, and cross pollinations. The desired isolation technique used detached culms in floral pics containing solutions of I9.53g sucrose and.195g 8 hydroxyquinoline citrate (8HQC)
TABLE OF CONTENTS Abstract List of Tables List of Figures i iii List of Plates.... iv 1. Introduction l 2. Objectives. 3 3. Literature Review.... 4 3.1. Origin 4 3.2. Morphology and Growth Habit. 12 3.3. Reproductive Biology of Plants... 15 3.3.1. Cross Fertilization 16 3.3.2. Self Fertilization... 17 3.4. Breeding Depression... 19 3.5. Reproductive Potential of Poa annua 22 3.6. Impact of Poa annua on Cultivated Turf... 28 4. Development of Pollination and Seed Ripening Techniques 31 4.1. Objective.................. 31 4.2. Materials and Methods 31 4.2.1. General Materials and Methods... 31 4.2.2. Influence of Leaf Removal on Seed Production of Excised Culms in Floral Pics 36 4.2.3. Sucrose plus 8 HQC versus Distilled Water. 37
4.2.4. One Percent Sucrose plus 100 ppm 8 HQC versus 2 Percent Sucrose plus 200 ppm 8 HQC.... 37 4.2.5. 500 versus 1000 ppm 8 HQC 38 4.2.6. Fructose versus Sucrose as Carbon Source.. 38 4.2.7. Environmental Influence.......... 39 4.2.8. Excised Culm Stem Length.......... 39 4.3. Results and Discussion... 40 4.4. Summary... 45 5. Analysis of Reproductive Biology of Poa annua. 4 6 5.1. Objective 46 5.2. Observations............ 46 5.2.1. Anthesis............. 46 5.2.1.1. Materials and Methods... 46 5.2.1.2. Results and Discussion.......... 47 5.2.2. Pollen Tube Growth. 4 8 5.2.2.1. Materials and Methods. 49 5.2.2.2. Results and Discussion. 50 5.2.3. Apomixis... 50 5.2.3.1. Materials and Methods..... 50 5.2.3.2. Results and Discussion.......... 51 5.3. Comparison of Self, Sib, and Outcross Seed Set,.,.. «*» *» -*2 5.3.1. Materials and Methods... 52 5.3.2. Results and Discussion... 54 5.3.2.1. Grand Means for Self, Sib, and Outcross Pairings... 54
5.3.2.2. Examples of Specific Genotypes Illustrating Outcrossing 55 5.3.2.3. Effects of Days between Panicle Excision and Anthesis 59 5.3.2.4. Effects of Anthesis Asynchrony between Paired Culms... 60 5.3.2.5. Effects of Number of Open Spikelets per Inflorescence., 63 5.3.2.6. Multiple Regression Analyses 63 5.3.2.6.1. Days between Excision and Anthesis... 67 5.3.2.6.2. Asynchronous Anthesis between Paired Culms 67 5.3.2.6.3. Number of Open Spikelets per Inflorescence 69 6. General Discussion 70 6.1. Methodology 70 6.2. Selfing versus Outcrossing.......... 71 6.2.1. Self Incompatibility............ 72 6.2.2. Incongruity.......... 73 6.2.3. Evolutionary Significance of Flexibility of Reproductive Mode 74 6.3. Further Experimentation 7 6 7. Summary 78 Tables................ 80 Figures........ 100 Plates * 108
Bibliography... Ill Appendix Al 121 Appendix A2. 131 Appendix A3... 136
LIST OF TABLES Table 1. Mean seed set per inflorescence for self- versus outcross- pollinated excised, paired culms isolated in pots. Table 2. Mean self seed set per inflorescence of bagged, selfed culms versus non-bagged open-pollinated culms. Table 3. Multiple regression file derivations. Table 4. Grand mean seed set per inflorescence of Poa annua culms, in floral pics, paired for self or outcross pollination. Table 5. Mean comparisons of self, sib, and outcross seed set of selected inflorescences matched for equal genotype representation. Table 6. Examples of self, sib, and outcross seed set per inflorescence or per open spikelet per inflorescence of genotypes grouped by families. Table 7. Examples of reduced outcross versus self seed set per open spikelet per inflorescence. Table 8. Examples of greater self versus outcross seed set per open spikelet per inflorescence. Table 9. Self and outcross seed set per open spikelet per inflorescence for AZ1716 and IL850006 used as females. Table 10. Incongruity and self incompatibility examples from selected diallel matings.
Table 11. Mean reproductive capacity expressed as seeds per inflorescence and as square root of seeds per square root of open spikelets per inflorescence, classified by elapsed days between culm excision and anthesis. Table 12. Reproductive capacity expressed as square root of seed set per square root of number of open spikelets per inflorescence of selected genotypes, classified by days elapsed between excision and anthesis. Table 13. Comparison of seed production per inflorescence pooled among genotypes and grouped by elapsed days between anthesis of paired culms. Table 14. Comparison of seed production per inflorescence pooled among genotypes and grouped by elapsed days between anthesis of paired culms. Table 15. Fluctuations in numbers of open spikelets per inflorescence between and within selected Poa annua genotypes. Table 16. Regression models for square root of seed set per inflorescence (SSDS) regressed on square root of number of open spikelets (SSPK), difference between excision and anthesis of female culms (BPOL), and geographic distance separating accessions origins (MILE). ii
LIST OF FIGURES Figure 1. Mean self seed production per inflorescence arranged by elapsed days between anthesis of paired culms. Genotypes included in this data set are not equally matched with genotypes used to construct Figure 2. Data summary is included in Table 13. Figure 2. Mean outcross seed production per inflorescence arranged by elapsed days between anthesis of paired culms. Genotypes included in this data set are not equally matched with genotypes used to construct Figure 1. Data summary is included in Table 13. Figure 3. Mean self seed production per inflorescence arranged by elapsed days between anthesis of paired culms. This subset of data included in Figure 1 contains comparable genotypes to those used in Figure 4. Data summary is included in Table 14. Figure 4. Mean outcross seed production per inflorescence arranged by elapsed days between anthesis of paired culms. This subset of data included in Figure 2 contains comparable genotypes to those used in Figure 3. Data summary is included in Table 14.
LIST OF PLATES Plate l. Examples of variability in growth habit of Poa annua L. On the left is a vigorously flowering, stoloniferous plant with light green color. The plant on the right is non-flowering, denser, and darker green. Plate 2. Protogynous inflorescence of Poa annua L. All stigmas of each floret in each spikelet are fully exposed for pollination prior to anther dehiscence from the same culm. Plate 3. Examples of excised culms paired for pollination isolation. The pair on the left consists of culms prior to anthesis. The inflorescences in the middle are at the peak of anthesis, with full panicle expansion. Stems on the right have fully mature seed ready for harvest. iv
1. INTRODUCTION Poa annua L., annual bluegrass, is often considered a weedy grass, yet it comprises a major turf component on many golf courses in temperate regions. In warm season grass areas of the United States, Poa annua is a winter annual. Perennial forms of "annual" bluegrass, Poa annua var. reptans Hausskn., are widespread (Hovin, 1957b; Tutin, 1957; Timm, 1965? Gibeault, 1971; Ellis, 1972; Wells, 1974; and Law et al, 1977). Poa annua biotypes, with potential for improvement for golf turf use, have been described (Cooper, 1957; Hovin, 1957c; Youngner, 1959; Beard, 1973; Adams and Bryan, 1977). Since this grass is difficult to eradicate, it would be desirable to combine preferred characteristics into selected perennial Poa annua types. To accomplish this, the reproductive biology must be evaluated in order to select breeding strategies for crop improvement. Poa annua has been reported to be self compatible with a low percentage of outcrossing (Hovin, 1957b; Tutin, 1957). The highest reported outcrossing level was 15 percent (Ellis et al, 1973). Self-, sib-, and cross- pollinated seed set from several related and unrelated accessions was used to 1
examine the variability and degrees of selfing or outcrossing which exist in Poa annua. This study of reproductive biology could also provide a model system from which it may be possible to generalize to other important species, such as the food crops, in Poaceae. Golf course managers, sod growers, and home owners who now encounter Poa annua invasions, caused by poor conditions, would benefit from development of grasses with desirable growth characteristics, rather than the weedy Poa annua of the field today. 2
2. OBJECTIVES 1. To develop an acceptable method for isolation of inflorescences used to obtain seed set data for reproductive biology analysis in Poa annua > 2. To determine selfing and outcrossing potentials in Poa annua by observation of morphology, anthesis, pollen tube development, apomixis, and seed yield from self, sib, and cross pollination. 3