Drought resistance and recovery mechanisms of tedera (Bituminaria bituminosa var. albomarginata)

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    [Truncated] Lucerne (Medicago sativa L.) often underperforms agronomically in Western Australia (WA), due to its sensitivity to acidic soils and the prolonged period of water stress during summer, which is typical of the WA Mediterranean climate. The development of new perennials adapted to acid soils and low rainfall is a high priority for future research in the Australian wheatbelt. Tedera (Bituminaria bituminosa var. albomarginata) is a recently-introduced herbaceous perennial legume that has shown potential as a drought-resistant forage species for Mediterranean environments across southern Australia and is currently being evaluated for domestication. Tedera is native to the Canary Islands of Spain and, on the island of Lanzarote, tedera can survive on as little as 150 mm per year, with a 5–6 month dry season.

    There have been no detailed investigations into drought adaptation and physiological traits of tedera in the field that have allowed this species to persist and be productive over summer. The mechanisms of drought resistance in legumes have not been characterised as well as in cereals. The objective of this thesis was to examine the drought resistance mechanisms of tedera under both field and controlled-environment conditions by comparing the response of tedera with lucerne. It is proposed that the drought resistance mechanisms of tedera are a combination of several morphological and physiological processes such as osmotic adjustment, an extensive root system, efficient stomatal control and paraheliotropism (leaf folding).

    Drought stress was initiated at different growth stages (seedling and mature plants) by withholding water in the controlled-environment study and by erecting a rain-exclusion shelter over summer in the field. Parameters relating to aboveground dry matter production, root growth, water-use efficiency, leaf-water relations, gas exchange, leaf folding, and individual leaf size were measured. The concentration of compatible solutes was determined for mature tedera plants in a controlled-environment study during both drought stress and recovery.

    The ability of seedlings to survive a drought following sowing or seedling germination in a regenerating pasture is important for successful pasture establishment/persistence. Thus, the first experiment (Chapter 2) was conducted under controlled-environment conditions (using soil reconstructed from the field) to investigate the physiological and morphological responses to water stress of tedera seedlings compared with lucerne, the annual pasture legume biserrula (Biserrula pelecinus L.) and the common summer-active weed Afghan melon (Citrullus lanatus Thunb). This study revealed significant differences in rooting depth and stomatal conductance among the three legume species when under water stress, with tedera being the most drought resistant. Key drought resistance traits in tedera included vigorous seedling growth, early taproot elongation, effective stomatal control and paraheliotropism. These traits may allow tedera seedlings to survive a dry period following opening autumn or winter rains.
    Original languageEnglish
    QualificationDoctor of Philosophy
    Publication statusUnpublished - 2015


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