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  • COMPARING CULTIVATED SUNFLOWER (HELIANTHUS) TO TWO WILD SPECIES FOR

    TRAITS PUTATIVELY ASSOCIATED WITH DROUGHT RESISTANCE

    by

    ETHAN FOSTER MILTON

    (Under the Direction of Lisa A. Donovan)

    ABSTRACT

    Drought is arguably the single greatest abiotic factor limiting plant productivity worldwide. Improving

    drought resistance of crops can counteract some of its detrimental effects. Identifying and incorporating

    variation from wild drought resistant congeners into crops is one avenue for improvement. We

    investigated two wild species of sunflower, Helianthus argophyllus (ARG) and H. niveus spp. tephrodes,

    (TEPH) hypothesized to be drought resistant and compared them to cultivated H. annuus (ANN) for

    drought resistance traits related to rooting, leaf and germination characteristics at various ontogenetic

    stages. Contrary to expectation, wild sunflowers did not outperform ANN for germination and rooting

    traits putatively associated with drought resistance, but TEPH exhibits leaf traits potentially useful in

    reducing heat load and water loss. Wild sunflowers do possess some traits that may potentially be useful

    for improving drought resistance in cultivated sunflower.

    INDEX WORDS: Drought, Sunflower, Ecophysiology, Germination

  • COMPARING CULTIVATED SUNFLOWER (HELIANTHUS) TO TWO WILD SPECIES FOR

    TRAITS PUTATIVELY ASSOCIATED WITH DROUGHT RESISTANCE

    by

    ETHAN FOSTER MILTON

    B.S., Florida State University, Tallahassee, 2007

    A Thesis Submitted to the Graduate Faculty of the University of Georgia in Partial Fulfillment

    of the Requirements for the Degree

    MASTER OF SCIENCE

    ATHENS, GEORGIA

    2013

  • 2013

    Ethan Foster Milton

    All Rights Reserved

  • COMPARING CULTIVATED SUNFLOWER (HELIANTHUS) TO TWO WILD SPECIES FOR

    TRAITS PUTATIVELY ASSOCIATED WITH DROUGHT RESISTANCE

    by

    ETHAN FOSTER MILTON

    Major Professor: Lisa A. Donovan

    Committee: John M. Burke

    Marc van Iersel

    Electronic Version Approved:

    Maureen Grasso

    Dean of the Graduate School

    The University of Georgia

    May 2013

  • iv

    TABLE OF CONTENTS

    Page

    LIST OF TABLES....vi

    LIST OF FIGURES.vii

    CHAPTER

    1 INTRODUCTIONAND LITERATURE REVIEW1

    References...6

    2 COMPARISON OF DESERT ADAPTED HELIANTHUS NIVEUS SSP. TEPHRODES

    TO CULTIVATED H. ANNUUS FOR PUTAITVE DROUGHT RESISTANCE TRAITS

    AT TWO ONTOGENETIC STAGES.9

    Abstract.10

    Introduction...11

    Materials and Methods..14

    Results...18

    Discussion.19

    References.25

    3 CULTIVATED HELIANTHUS ANNUUS AND WILD RELATIVES (H.

    ARGOPHYLLUS AND H. NIVEUS SSP. TEPHRODES) DIFFER IN GERMINATION

    RESPONSE TO SIMULATED DROUGHT STRESS.46

    Abstract.47

    Introduction...48

    Materials and Methods..51

    Results...53

    Discussion.54

  • v

    Page

    References.59

    4 CONCLUSIONS ......72

  • vi

    LIST OF TABLES

    Page

    Table 2.1: Distribution of seedling means ( SE) for two species of Helianthus (sunflower),

    H. annuus and H. niveus ssp. tephrodes for measured traits...33

    Table 2.2: Distribution of mature means ( SE) for two species of Helianthus (sunflower),

    H. annuus and H. niveus ssp. tephrodes for measured traits.......34

    Appendix Table 2.1: Distribution of means for normalized difference vegetative index (NDVI)

    components R680 and R800 with associated standard error between two species of Helianthus

    (sunflowers).....45

    Table 3.1: Percent germination (% Germ) and mean germination time (MGT) (means + SE) for

    three species of Helianthus (sunflowers), H. annuus (ANN), H. argophyllus (ARG) and H. niveus

    ssp. tephrodes (TEPH) for polyethylene glycol 6000 induced water stress treatments............66

    Table 3.2: Likelihood ratio contrasts of standardized species Helianthus annuus (ANN),

    H. argophyllus (ARG) and H. niveus ssp. tephrodes (TEPH) germination time regressions for

    polyethylene glycol 6000 induced water stress treatments......67

  • vii

    LIST OF FIGURES

    Page

    Figure 2.1: Comparison of Helianthus annuus (ANN) and H. niveus ssp. tephrodes (TEPH) at the

    seedling stage for measured traits....29

    Figure 2.2: Comparison of Helianthus annuus (ANN) and H. niveus ssp. tephrodes (TEPH) at

    the mature stage for measured traits....31

    Appendix Figure 2.1: Comparison of Helianthus annuus seedling accession means for measured

    traits..............35

    Appendix Figure 2.2: Comparison of Helianthus niveus ssp. tephrodes seedling accession means

    for measured traits. ..........37

    Appendix Figure 2.3: Comparison of Helianthus annuus mature accession means for traits

    measured..........39

    Appendix Figure 2.4: Species means for normalized difference vegetative index (NDVI) components

    at the seedling stage....41

    Appendix Figure 2.5: Species means for normalized difference vegetative index (NDVI) components

    at the mature stage....42

    Appendix Figure 2.6: Comparison of Helianthus niveus ssp. tephrodes mature accession means

    for traits measured............43

    Figure 3.1: Percent germination after seven days for three species of Helianthus (sunflower)

    H. annuus (ANN), H. argophyllus (ARG) and H. niveus ssp. tephrodes (TEPH) for polyethylene

    glycol 6000 induced drought stress treatments.63

    Figure 3.2: Mean germination time after seven days for three species of Helianthus (sunflower)

    H. annuus (ANN), H. argophyllus (ARG) and H. niveus ssp. tephrodes (TEPH) for polyethylene

    glycol 6000 induced water stress treatments.64

  • viii

    Page

    Figure 3.3: Probability density functions for observed germination frequency by day for three

    species of Helianthus (sunflower) H. annuus (ANN), H. argophyllus (ARG) and H. niveus ssp.

    tephrodes (TEPH) for polyethylene glycol 6000 induced water stress treatments...65

    Appendix Figure 3.1: Percent germination after seven days for accessions of three species of

    Helianthus (sunflower) H. annuus (ANN), H. argophyllus (ARG) and H. niveus ssp. tephrodes

    (TEPH) for polyethylene glycol 6000 induced drought stress treatments............68

    Appendix Figure 3.2: Mean germination time after seven days for accessions of three species of

    Helianthus (sunflower) H. annuus (ANN), H. argophyllus (ARG) and H. niveus ssp. tephrodes

    (TEPH) for polyethylene glycol 6000 induced drought stress treatments........70

  • 1

    CHAPTER 1

    INTRODUCTION AND LITERATURE REVIEW

    The availability of water is arguably the single largest abiotic factor that affects productivity in

    both natural and agronomic systems (Boyer 1982; Blum 1996; Passioura 1996; Verslues, Agarwal et al.

    2006). Abiotic stress, specifically drought, is topic of great concern given the expectation that under

    global warming many areas will experience a change in precipitation patterns and an increase in extreme

    temperatures. These meteorological changes will bring with them an increase in duration, frequency and

    severity of drought (Houghton, Ding et al. 2001; IPCC 2007). Thus there exists an emerging need to

    make crops more resistant to the detrimental effects of drought. Crop species and their wild congeners

    have long been a focus of study in applied biology. The identification of traits useful for resource uptake,

    allocation, reproduction as well as resistance to biotic and abiotic stress has provided insights into the

    potential for improving commercial crops (Ashraf and O'Leary 1996). A thorough understanding of

    physiological traits associated with drought resistance and improved water use efficiency is crucial for

    crop improvement (Ashraf and O'Leary 1996; Passioura 2006; Richards 2006). One potential source for

    crop improvement in terms of drought resistance is to identify putative drought resistance traits and

    incorporate wild germplasm from species adapted to water stressed environments.

    Drought is defined as a prolonged period that is characterized by the absence of precipitation or

    supplemental water supply and results in declining soil water availability (Boyer 1982). Broadly defined,

    drought resistance is the ability of plants to deal with decreasing soil water availability (lower or more

    negative soil water potential) either through internal or external mechanisms. Plants have three strategies

    to cope with or resist declining soil water availability (Kramer and Boyer 1995): escape, avoidance and

    tolerance. This thesis focuses on drought avoidance and drought tolerance, using the terminology most

    consistent with Levitt (Levitt 1980) and Verslues (Verslues, Agarwal et al. 2006).

  • 2

    Drought avoidance is a plants ability to avoid lower internal water potentials even though soil

    water potential is declining, by maintaining a favorable balance of water uptake to water loss (Verslues,

    Agarwal et al. 2006). This can be achieved with both inh

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