Date of Award:

12-2020

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Plants, Soils, and Climate

Department name when degree awarded

Plant, Soils and Climate

Committee Chair(s)

Bruce Bugbee

Committee

Bruce Bugbee

Committee

Brent Black

Committee

Scott Jones

Committee

Andrew Kulmatiski

Committee

Niel Allen

Abstract

New orchard plantings utilize trees grafted to dwarfing rootstocks planted close together to facilitate larger harvests. These dwarfing rootstocks have not been comprehensively studied for their ability to withstand drought. This is of special importance in the Intermountain West which has limited rainfall. Additionally, orchard growers face competition for water from a growing population and increased uncertainty in rainfall from climate change. My research examined the use of dendrometers, which measure changes in trunk diameter, and sap flow sensors, which measure how quickly sap moves, as methods to inform growers about tree water status. I also used a weighing lysimeter system to measure tree water use in four different rootstocks as they were subjected to drought.

In a field study, I placed dendrometers and sap flow sensors in a high-density apple orchard. As the trees progressed through the season and put on fruit the responses from the sensors changed. By separating data from the sap flow sensors and dendrometers into seasons, their ability to predict tree water status improved. I found that overall dendrometers would be the best way to automate measurements of tree water status.

In my first rootstock trial I examined responses of peach trees grown from seeds from an orchard maintained by Navajo farmers in South Western Utah, and a commercially available rootstock. I found that the Navajo peach trees put on more growth than the commercial trees despite drought, which suggests that they may be useful for rootstock development. In my second rootstock trial I examine the commercially available Krymsk® 5 and 6 series dwarfing cherry rootstocks for responses to drought. I found that the Krymsk® 6 rootstocks had higher rates of transpiration and used water faster than the Krymsk® 5 allowing them to put on growth quickly even during drought. Krymsk® 5 rootstocks have a lower percentage of their biomass in their roots which may have helped to conserve water.

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