Masters Theses

Date of Award

12-2001

Degree Type

Thesis

Degree Name

Master of Science

Major

Entomology and Plant Pathology

Major Professor

Mark T. Windham

Committee Members

Alan Windham, William Klingeman, Craig Canaday

Abstract

Canker diseases of Leyland cypress, x Cupressocyparis leylandii (A.B. Jacks. & Dallim.) Dallimore, caused by Seiridium unicorne (Cooke & Ellis) Sutton and Botryosphaeria dothidea (Moug.: Fr.) Ces.& De Not. are becoming common in the Southeast. Symptoms include cankers, resinosis, and branch dieback. Little is known about which pathogen is more prevalent in Tennessee and if canker diseases may be influenced by site parameters or environmental conditions. Canker development is thought to be increased when plants are predisposed to moisture stress. Drought stress is thought to significantly influence canker development compared to flooding stress. The objectives of this research were to: 1) determine which pathogen is more prevalent at various sites across Tennessee, 2) determine if site factors were correlated with pathogens found on site, 3) determine if predisposing Leyland cypress to moisture stress intensified susceptibility to Seiridium or Botryosphaeria, 4) determine if pathogens affected growth of trees inoculated, and 5) compare the pathogenicity of Seiridium and Botryosphaeria species.

Leyland cypress samples were collected at 17 sites throughout Tennessee. Symptomatic branches were collected, placed in moisture chambers, and fungi isolated were identified using light microscopy. S. unicorne was the only species of Seiridium found in Tennessee. S. unicorne was isolated more frequently on diseased Leyland cypress than B. dothidea.

Tree and site characteristic data including diameter at breast height (DBH), soil in pH, tree height, tree spacing, slope, available water, and overall appearance of tree were recorded. Although site slope (R = 0.0345), tree spacing (R = 0.0393), and DBH (R = 0.0059) were correlated with isolation of S. unicorne (P = 0.05), the relationship was not strong. No other site factors (available water, height, pH, and disease scale) had a significant correlation with isolation of S. unicorne. Soil pH was correlated with isolation of B. dothidea (R = 0.0180, P = 0.05). The relationship was not strong, therefore additional research should be completed before proper conclusions can be drawn comparing site parameters and pathogen incidence on sites.

To determine if predisposition of moisture stress influenced canker development, ninety Leyland cypress trees were purchased and predisposed to different stress regimens (drought, normal, and flooding). Trees were inoculated with isolates of S. unicorne or B. dothidea. Trees were evaluated for eight weeks and data such as height, caliper, and canker length (interior and exterior) were recorded. This experiment was completed twice in greenhouses with a completely randomized design.

Seiridium unicorne was found to be more virulent than B. dothidea on Leyland cypress in this experiment. Interior canker length caused by S. unicorne was longer than B. dothidea. Trees inoculated with Seiridium spp. exhibited more branch dieback and resinosis than Botryosphaeria spp. inoculated trees. B. dothidea in previous studies caused similar symptoms on Leyland cypress as Seiridium species. Drought stress significantly increased Seiridium canker development whereas flooding stress did not influence canker development. Moisture stress treatments did not significantly affect plants inoculated with B. dothidea.

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