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Title: Inducing defoliation and dormancy of juvenile nursery trees in a changing climate
Author: Ward, Neal
ISNI:       0000 0004 2726 8103
Awarding Body: University of Reading
Current Institution: University of Reading
Date of Award: 2011
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Reduced or delayed natural leaf fall in autumn can interfere with lifting and marketing of nursery trees. Warmer autumns associated with climate change may exacerbate this problem. The aim of this research was to investigate how abiotic factors interact to promote leaf abscission in juvenile trees, and how management strategies, such as the use of defoliants, could enhance abscission. Experiments were implemented on Rosaceae species to develop a generic model to predict leaf abscission. The effectiveness of copper as a defoliant (as Cu. EOTA) was strongly dependant on time and leaf age; greatest defoliation in Crataegus monogyna being associated with later (Sep and Oct) applications and older leaves. There was evidence that Cu EOT A acted both directly on abscission zone cells (possibly through cell wall loosening), as well secondary pathways involving tissue damage and ethylene evolution. Applying supra-optimal Cu2+ concentrations, however, reduced ethylene evolution, suggesting high concentrations may actually inhibit ethylene synthesis. Prolonged chilling '(O-l0°C) was more effective at inducing defoliation than frost (<0°C), contravening conventional thinking that ice formation per se is important Temperature interacted with other physiological factors, however. Chilling for 900 hours (6-10°C) reduced chlorophyll content, abscission zone break-strength and polar auxin transport (PAT) capacity in the leaf petiole compared to 30 or 300 hours of chilling, or short periods of frost (-2°C). Chemically reducing PAT from the shoot apex using localised applications of 2,3,5- triiodobenzoic acid (TIBA) had mixed effects; TIBA+frost increased defoliation; however TIBA+chilling did not. Replacing chilling stimuli with non-lethal water deficit or wateriogging significantly enhanced leaf abscission, with waterlogging being more effective than deficit. A model relying on the additive effects of a number of stimuli is discussed, whereby in the absence of one stimulus (e.g. chilling), another (e.g. water stress) may help induce abscission.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available