Date of Award:

5-2018

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Biology

Committee Chair(s)

Claudia Nischwitz

Committee

Claudia Nischwitz

Committee

Larry Rupp

Committee

Bradley Kropp

Abstract

The black walnut, Juglans nigra L., is native to the United States (USA) and is a valuable timber and nut tree. Just before the beginning of the 21st century, several western states observed a decline in the health and, later, death of black walnut trees. The pathogen-vector complex now known as thousand cankers disease (TCD) was shown to be the cause. The disease, caused by Geosmithia morbida Kolařik, is vectored by the walnut twig beetle (WTB), Pityophthorus juglandis Blackman. Thousands of WTB will swarm and enter a tree vectoring the fungus at each entry point where cankers then develop, quickly expand, coalesce and kill the branch or stem. The disease has been confirmed across the USA and in parts of Europe. The research and development of resistant cultivars is important to maintain native populations and livelihoods. The purpose of this project was to evaluate black walnut and hybrid trees for resistance to TCD through direct inoculation with the pathogen G. morbida. Inoculation of limbs took place in early summer of 2015, 2016 and 2017 at the Cyril Reed Funk Research Farm in Richmond, UT and Dayton, ID. Inoculated limbs were removed from the tree after senescence and canker size measured. An average of 336 trees were inoculated. One tree consistently exhibited resistance to TCD indicated by no canker staining. An additional 14 trees exhibited resistance for two of the three years. The results of this project indicate that breeding for resistance to TCD could be a management option for the disease.

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