Dissertation Defence: Aspects of Low Temperature Survival in Sweet Cherry (Prunus avium) in the Okanagan Valley

Elizabeth Anne Houghton, supervised by Dr. Louise Nelson & Dr. Kirsten Hannam, will defend their dissertation titled “Aspects of Low Temperature Survival in Sweet Cherry (Prunus avium) in the Okanagan Valley” in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Biology.

An abstract for Elizabeth Anne Houghton’s dissertation is included below.

Examinations are open to all members of the campus community as well as the general public. Registration is not required for in person exams.

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ABSTRACT

Sweet cherry (Prunus avium) is a perennial fruit tree with horticultural importance in the Okanagan Valley, British Columbia. In the Okanagan Valley, climate change is expanding suitable growing regions for sweet cherry; crop establishment in more extreme locations and increased frequency of extreme weather events raise concerns for the availability of sufficient irrigation water and crop winter survival. There is also a need for tools to help growers mitigate crop cold damage and gaps in current knowledge of factors that influence overwintering flower bud cold hardiness estimates and freezing survival mechanisms (supercooling).

My research investigated the response of ‘Sweetheart’/Mazzard sweet cherry trees to postharvest deficit irrigation (PDI) in five commercial Okanagan Valley orchards. I found that reducing postharvest irrigation by up to 50% volumetrically, compared to full irrigation at growers’ practice, did not significantly affect tree growth, flower spring phenology or cold hardiness in the seasons following PDI application. I developed models to estimate sweet cherry flower bud cold hardiness and an open-access web application for easy use of these models as a cold damage mitigation decision support tool. I also evaluated the influence of different differential thermal analysis (DTA) methodologies on flower bud cold hardiness estimates and compared DTA and controlled freezing test estimates. Buds stored at warmer temperatures, transported in moist environments, and exposed to faster cooling rates experienced biologically relevant losses in cold hardiness when estimated using DTA. DTA and controlled freezing tests provided comparable cold hardiness measures. Finally, I investigated flower bud supercooling mechanisms. I observed that ice nucleation barriers appeared to be primordium specific, ice was accommodated within the bud scales and bud axis (but supercooling was not dependent on bud scale presence), and disturbing the region subtending the primordia interfered with supercooling. Furthermore, vascular differentiation in the primordia was correlated with the loss of supercooling in the spring. Study findings support that sweet cherry flower buds undergo extraorgan freezing. Overall, this work has contributed to an improved understanding of PDI as a sustainable irrigation strategy and the dynamics of, methodologies used to estimate, and properties that promote supercooling in overwintering sweet cherry flower buds.