Date of Award:

5-2022

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Plants, Soils, and Climate

Department name when degree awarded

Plant, Soils, and Climate

Committee Chair(s)

Teryl Roper

Committee

Teryl Roper

Committee

Brent Black

Committee

Grant Cardon

Abstract

Apple trees are susceptible to biotic and abiotic stresses in the Intermountain West. The arid climate along with non-ideal soils make apple production challenging. Also, as high-quality agricultural land is developed, crop production gets pushed to land that often is saline. Apple trees grow poorly in saline soils. If apples are going to be grown in Utah, rootstocks must be identified that will tolerate saline soils. The USDA rootstock breeding program produced some rootstocks that may show salt tolerance. This project assessed the salt tolerance of these apple rootstocks in the greenhouse and in the field. Test rootstocks were compared to M.9, a widely planted apple rootstock. In greenhouse tests, a near-continuous gradient dosing system was used to screen 19 apple rootstocks for tolerance to calcium chloride salinity. All of the rootstocks showed a decrease in height, fresh weight, and dry weight as salt concentration increased. Three field test locations were used: Kaysville had minimal salt, Goshen had sodium salt, and Tintic had calcium salt. Over two seasons, field studies showed that sodium salts reduced tree height and trunk cross sectional area more than calcium salts. No rootstock performed significantly better than M.9 in either the field or greenhouse.

Bitter pit is a calcium related disorder of apples that often develops in storage. Affected apples have sunken dark spots on the peel and are unmarketable. The incidence of bitter pit is not uniform across apple rootstocks because apple rootstocks vary in their ability to partition calcium to fruit. Apples from 14 rootstocks in the 2014 NC-140 planting were examined for bitter pit incidence following storage at 4°C. In general, vigorous rootstocks showed lower peel calcium and a higher incidence of bitter pit following storage.

Tree suckers can potentially harbor disease and insects in orchards. Removing suckers is important but expensive because of the labor required. Finding other cost-effective ways can help growers. Paraquat, fire, naphthalene acetic acid, and urea ammonium nitrate (UAN) were compared along with water for sucker control. UAN provided excellent, but not long lasting, sucker suppression.

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