Pollination Biology of Echinacea Angustifolia and Echinacea Purpurea (Asteraceae) in Saskatchewan
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Pollination biology of Echinacea angustifolia and Echinacea purpurea (Asteraceae) in Saskatchewan A thesis submitted to the College of Graduate Studies and Research in Partial Fulfillment of the Requirements for the degree of Master of Science in the Department of Biology University of Saskatchewan Saskatoon, Saskatchewan, Canada By Tyler J. Wist ©Copyright Tyler J. Wist, October 2005 All rights reserved. PERMISSION TO USE In presenting this thesis in partial fulfillment of the requirements for a Postgraduate degree from the University of Saskatchewan, I agree that the Libraries of this University may make it freely available for inspection. I further agree that permission for copying of this thesis in any manner, in whole or in part, for scholarly purposes may be granted by the professor or professors who supervised my thesis work or, in their absence, by the Head of the Department or the Dean of the College in which my thesis work was done. It is understood that any copying or publication or use of this thesis or parts thereof for financial gain shall not be allowed without my written permission. It is also understood that due recognition shall be given to me and to the University of Saskatchewan in any scholarly use which may be made of any material in my thesis. Requests for permission to copy or to make other use of material in this thesis in whole or part should be addressed to: Head of the Department of Biology University of Saskatchewan Saskatoon, Saskatchewan S7N 5E2 i ABSTRACT The goals of this research project were to identify the various insects observed to visit inflorescences of Echinacea angustifolia DC, and to rank these visitors according to their importance as pollinators of E. angustifolia in Saskatchewan. Studying nectar and the nectary is essential to understanding the interaction of disc florets with pollinators. Nectar-sugar production by disc florets of E. angustifolia and E. purpurea (L. Moench) was quantified from anthesis to cessation with production per disc floret peaking in the afternoon of the staminate phase (191.7 µg) and at midday of the first day of the pistillate phase (156.6 µg), respectively. Morphology of the disc-like floral nectaries of both Echinacea species was studied, as well as the ultrastructure of the nectary of E. purpurea. Modified stomata on the nectary rim are the most likely exits for nectar, but creases in the epidermis may also participate. The nectary of E. purpurea is vascularized by phloem alone, which occurred adjacent to the epidermis. Companion cells possessed wall ingrowths, and these cells may unload arriving sugar destined for either an apoplastic or symplastic pathway. Lobed nuclei were a key feature of secretory parenchyma cells, as was a predominance of mitochondria, suggesting that energy-requiring eccrine secretion predominates in E. purpurea. E. angustifolia exhibited a generalist pollination system, with pollinating insects belonging to the orders Coleoptera, Diptera, Hymenoptera, and Lepidoptera. The pollination efficiency of visitors was determined by single insect visits to bagged, virgin inflorescences followed by quantifying pollen tubes at the bases of receptive styles and/or calculating the percentage of shrivelled styles. It was determined that bumble bees (Bombus spp.) were efficient pollinators, indicating that they would likely contribute much to the pollination of E. angustifolia. Grasshopper bee flies (Systoechus vulgaris Loew) were plentiful but individually were not efficient pollinators, but taken together, they provided much pollination. Golden blister beetles (Epicauta ferruginea Say) were efficient pollinators but where yellow-petalled flowers occurred, their numbers on E. angustifolia decreased. Honey bees (Apis mellifera L.) were efficient pollinators and were present in low numbers without managed introduction. Pierid (2003) butterflies were regular visitors and efficient pollinators, and likely contributed ii significantly to E. angustifolia pollination. When introduced, the alfalfa leafcutter bee (Megachile rotundata Fabr.) preferred not to forage on E. angustifolia and as such, these solitary bees were not suitable as managed pollinators. In large agricultural plantings of E. angustifolia, however, native insects may not be capable of providing sufficient pollination for seed production when floral competition occurs. iii ACKNOWLEDGEMENTS I wish to thank my supervisor, Dr. Arthur R. Davis, for his patience, guidance, revision expertise, valuable time and mentoring skills. Thank you as well to my advisory committee members Dr. Branka Barl and Dr. Robert Randell for their valuable input and comments and for the time that they have dedicated to meetings and reviewing committee reports and this thesis. I wish to thank the individuals and organizations that allowed me access to their Echinacea angustifolia fields; the staff at Prairie Plant Systems Inc., Meewasin Valley Authority, and Doug Pchajek. Many individuals contributed in certain ways to this project and I wish to thank my field assistant Jason Wolfe, William Hrycan for computer technical assistance, Daryn Bikey for his contributions to HPLC and data entry, Jeaniene Smith for assistance in the greenhouse and growth chamber and Dennis Dyck for his photographic and presentation expertise. Special thanks to Wayne Goerzen and Gaylord Mirau of SASPA for providing the materials and bees for the alfalfa leafcutter bee trials. Very special thanks go to my wife Rachelle who has supported me through this project and helped with field and lab work whenever she was able. I would like to acknowledge funding for this project from the University of Saskatchewan in the form of a University Graduate Scholarship and a Graduate Teaching Fellowship and partial funding from the Agri- Food Innovation Fund and the Natural Sciences and Engineering Research Council of Canada in the form of grants to Dr. A. R. Davis. iv TABLE OF CONTENTS PERMISSION TO USE ...................................................................... i ABSTRACT......................................................................................... ii ACKNOWLEDGEMENTS ................................................................ iv TABLE OF CONTENTS .................................................................... v LIST OF TABLES............................................................................... ix LIST OF FIGURES ............................................................................. x Chapter 1: INTRODUCTION 1.1 Specialty crops and Echinacea 1 1.1.1 Echinacea species grown in Saskatchewan 2 1.1.2 General morphology of Echinacea angustifolia and E. purpurea 3 1.1.3 Nectar and asteracean nectaries 4 1.2 Insect pollination of crop plants 5 1.2.1 The value of honey bee pollination and current challenges 6 1.2.2 Native pollinators and current challenges 7 1.2.3 Breeding system in Echinacea 9 1.3 Project objectives 11 Chapter 2: FLORAL MORPHOLOGY, NECTARY ANATOMY AND ULTRASTRUCTURE AND NECTAR SECRETION BY DISC FLORETS 2.1 Introduction 13 2.2 Materials and Methods 14 2.2.1 Plant material and field sites 14 2.2.1.1 Meewasin Valley Authority’s Chief Whitecap Park 15 2.2.1.2 Valley Road 15 2.2.1.3 W.P. Thompson (Biology) garden plot and growth chamber 16 2.2.2 Phenology and morphology of ray and disc florets of the capitulum 16 2.2.2.1 Pollen grain counts 16 2.2.2.2 Pollen grain cytology 17 2.2.2.3 Pollen viability 17 2.2.3 Disc floret structure and nectary ultrastructure 18 2.2.3.1 Scanning electron microscopy 18 2.2.3.2 Light and transmission electron microscopy 18 2.2.4 Nectar dynamics during floret phenology 19 2.2.4.1 Nectar volumes 20 2.2.4.2 Nectar-sugar concentrations 20 2.2.4.3 Nectar-sugar quantities per disc floret 20 2.2.4.4 Nectar-carbohydrate composition 20 v 2.3 Results 21 2.3.1 Phenology and morphology of ray and disc florets 21 2.3.1.1 Ray florets 21 2.3.1.2 Phenology of disc floret development 21 2.3.1.3 Disc floret morphology 22 2.3.1.3.1 Calyx 22 2.3.1.3.2 Corolla 26 2.3.1.3.3 Androecium 26 2.3.1.3.3.1 Pollen grain structure 26 2.3.1.3.3.2 Pollen grain counts 29 2.3.1.3.3.3 Pollen viability 29 2.3.1.3.4 Gynoecium 29 2.3.1.3.5 Nectary morphology, anatomy and ultrastructure 30 2.3.1.3.5.1 Epidermis 30 2.3.1.3.5.2 Nectary vasculature 36 2.3.1.3.5.3 Parenchyma cells 39 2.3.2 Dynamics of nectar secretion: Echinacea purpurea 45 2.3.2.1 Nectar volume 45 2.3.2.2 Nectar-solute concentrations 45 2.3.2.3 Nectar-sugar quantity 45 2.3.2.4 Nectar-carbohydrate composition 46 2.3.3 Dynamics of nectar secretion: Echinacea angustifolia 48 2.3.3.1 Nectar volume 48 2.3.3.2 Nectar-solute concentrations 49 2.3.3.3 Nectar-sugar quantity 49 2.4 Discussion 51 2.4.1 Characteristics of reproductive structures of E. angustifolia and E. 51 purpurea 2.4.1.1 Inflorescence morphology and flowering phenology 51 2.4.1.2 Disc floret morphology 52 2.4.1.3 Pollen morphology 52 2.4.1.4 Calyx 53 2.4.1.5 Gynoecium 53 2.4.1.6 Nectary 55 2.4.1.6.1 Nectary morphology 55 2.4.1.6.2 Modified stomata 56 2.4.1.6.3 Anatomy of the floral nectary of E. purpurea 57 2.4.1.6.3.1 Nectary phloem 57 2.4.1.6.3.2 Parenchyma cells of the nectary 60 2.4.1.6.3.3 Features of modified stomata on the nectary surface 62 2.4.1.6.3.4 Pathway of pre-nectar to the nectary exterior 63 2.4.2 Phenology and nectar-production dynamics 64 vi Chapter 3: INSECT POLLINATION OF ECHINACEA ANGUSTIFOLIA 3.1 Introduction 69 3.1.1 Excluder cage experiments 71 3.1.2 Pollen tube counts 73 3.1.3 Shrivelled style estimate of pollination 74 3.2. Materials and Methods 76 3.2.1 Field sites 76 3.2.1.1 Prairie Plant Systems 76 3.2.1.2 Meewasin Valley Authority 76 3.2.1.3 Valley Road 76 3.2.2.