Poinsettia (Euphorbia Pulcherrima Willd. Ex Klotzsch: Euphorbiacea)
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Poinsettia (Euphorbia pulcherrima Willd. ex Klotzsch: Euphorbiacea) Resistance Mechanisms against the Silverleaf Whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) Biotype B DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Karla J. Medina-Ortega, M.S. Graduate Program in Entomology The Ohio State University 2011 Dissertation Committee: Dr. Luis Cañas, Advisor Dr. Daniel A. Herms Dr. P. Larry Phelan Dr. Claudio Pasian Copyright by Karla Jacqueline Medina Ortega 2011 Abstract The silverleaf whitefly (Bemisia tabaci biotype B) is the main above-ground insect pest of poinsettias (Euphorbia pulcherrima). The ornamental industry is important to the economy of the U.S. and among potted plants, poinsettias rank first in sales across the nation. Control of whiteflies in greenhouses is primarily with insecticides; therefore, mechanisms of resistance in poinsettias are not well understood and have not been thoroughly studied. In an effort to elucidate defense mechanisms in poinsettias, both physical and chemical traits of the plant were studied. The goal of this research was to determine if poinsettia cultivars possess factors/traits affecting the behavior and physiology of the silverleaf whitefly and to some extent evaluate tritrophic interactions. The objectives were to (1) determine silverleaf whitefly behavioral preference for, and performance on different cultivars through choice and no-choice assays (Chapter 2); (2) evaluate physical traits possibly mediating resistance, including visual cues by excluding light, leaf thickness, and leaf color indirectly via chlorophyll content using a SPAD meter, and with the use of a color reader (Chapter 2); (3) determine free amino acids and phenolic compounds potentially involved in mediating resistance to B. tabaci (Chapter 3); (4) evaluate tritrophic interactions by comparing Eretmocerus mundus ii parasitism preference between B. tabaci nymphs from a more and a less susceptible poinsettia cultivars (Chapter 4). Behavioral preference of B. tabaci varied among cultivars, but cultivars with light green leaves were preferred than cultivars with dark green leaves. Leaf color appeared to be influenced by chlorophyll content and leaf thickness. Cultivars with light green leaves had less chlorophyll and had thinner leaves. Trichome density was not significantly different among the cultivars. While whiteflies were capable of recognizing a more susceptible host in the presence of light, this was not the case when in the absence of it indicating leaf color of poinsettia plants plays a key role in recognition by B. tabaci. Phloem chemistry revealed that cultivars were similar in the composition and concentration of amino acids, and cultivars with light green leaves averaged a higher concentration of amino acids. No differences, although, were observed in concentration of essential amino acids. While concentration of individual amino acids differed in ways that did not help to explain patterns of resistance, concentration of individual phenolic compounds, in both leaf and petioles, did correspond with patterns of resistance to B. tabaci. Total concentration of phenolics were higher in a less susceptible cultivar (cv [‗Freedom Red‘]) with dark green leaves, and where fertility of B. tabaci was lower, than on a more susceptible cultivar (‗Monet Twilight‘) with light green leaves where fertility of B. tabaci was higher. Concentrations of over 45 % of individual phenolics shared between the two cultivars were higher in ‗Freedom Red‘. While ‗Freedom Red‘ had four unique compounds, only one compound was unique to ‗Monet Twilight‘. Compounds unique to, and in higher amount in ‗Freedom Red‘ included galloyl quinic acids, digalloyl iii glucose, apigenin diglucoside, apigenin glucoside, kaempferol hexoside, and quercetin pentose rutinoside, and rutin. These compounds have been associated with resistance to herbivores, prolonging developmental times, and acting as antifeedants and toxins. Higher parasitism of B. tabaci nymphs on cv ‗Monet Twilight‘ was observed than on cv ‗Freedom Red‘. More studies are needed to determine if preferences of parasitism are due to the host plant itself or the nymphs to understand the dynamic interactions of bottom-up and top-down factors; also more in-depth analysis comparing the ratio of amino acids and phenolic compounds in more and less susceptible poinsettia cultivars in relation to the behavior and physiology of both whiteflies and its parasitoids needs to be conducted to better understand their ecological role in this system. iv Dedication To my parents and sisters, my pillars! And to my dear love Justin Whitehill for giving sense to my life! v Acknowledgments I thank Justin Whitehill first of all for all his support and guidance in most of this journey—without you this journey would have not been the same. I thank my committee members Luis A. Cañas, Larry Phelan, Daniel Herms, and Claudio Pasian for their guidance through all my degree. Luis A. Cañas was more than an advisor to me, thank you for your friendship. Larry Phelan, your valuable mentorship and critical thinking will always be with me. Daniel Herms, thank you for your constructive feedback and critical thinking principles as well. Claudio Pasian, thank you for your support and help. I thank also Pierluigi Bonello for the use of his HPLC and an office in Plant Pathology my last months‘ writing this dissertation. I thank Claudia Kuniyoshi and Nuris Acosta for their invaluable friendship, so many entertaining afternoons and help throughout my degree. I thank my dear friend Ronald Batallas and Rodrigo Chorbadjian for being a great moral support. I thank all my friends from Entomology including Brenda Franks, who was so special and kind always, all of you made better my living at Wooster. I thank the help of Wilmer Rodríguez, Jim Hacker, Mark Belcher, Alejandro Paz, Eliana Rosales, Alejandra Claure, Samuel Discua, Diego Rincón, Theodore Derksen, Gabriel Abud, and David Abud for help in collecting data. vi Vita November 30th, 1979 ......................................Tegucigalpa, Honduras 2000................................................................B.S. Agriculture, Escuela Agrícola Panamericana, El Zamorano, Honduras 2001................................................................Research Scholar, Illinois Natural History Survey, University of Illinois at Urbana- Champaign 2002................................................................Research Scholar, CABI, Switzerland 2003................................................................Field and Laboratory Research Scientist, Escuela Agrícola Panamericana, El Zamorano, Honduras 2005................................................................M.S. Entomology, University of Idaho Apr-Sept 2006 ................................................Graduate Research Associate, Department of Entomology, The Ohio State University Oct 2006-Jun 2007 .........................................Graduate Teaching Associate, Department of Entomology, The Ohio State University Jul 2007-Mar 2011 .........................................Graduate Research Associate, Department of Entomology, The Ohio State University Apr 2011-present ...........................................Graduate Teaching Associate, Department of Entomology, The Ohio State University vii Publications Medina-Ortega, K.J., Bosque-Pérez, N.A., Ngumbi, E., Jiménez-Martínez, E.S., and Eigenbrode, S.D. 2009. Rhopalosiphum padi (Hemiptera: Aphididae) responses to volatiles cues from barley yellow dwarf virus-infected wheat. Environ. Entomol. 38(3): 836-845. Fields of Study Major Field: Entomology viii Table of Contents Abstract ............................................................................................................................... ii Dedication ............................................................................................................................v Acknowledgments.............................................................................................................. vi Vita .................................................................................................................................... vii Publications ...................................................................................................................... viii Fields of Study ................................................................................................................. viii Table of Contents ............................................................................................................... ix List of Tables ..................................................................................................................... xi List of Figures ................................................................................................................... xii Chapter 1 Literature Review ................................................................................................1 General background .......................................................................................................1 Statement of the problem ...............................................................................................3 Research foci ..................................................................................................................4 Poinsettias ......................................................................................................................5