Ailanthus altissima Wilt and Mortality: Etiology

Area of Science:

• Forest Pathology
• Plant-Microbe Interactions
• Invasive Species Management

Background:

• An unprecedented epidemic of wilt and mortality affecting invasive tree-of-heaven (Ailanthus altissima) has been observed in Pennsylvania's mixed-hardwood forests.
• The causal agent of this extensive tree-of-heaven die-off remained unidentified prior to this investigation.

Purpose of the Study:

• To identify the pathogen responsible for the widespread mortality of invasive tree-of-heaven in south-central Pennsylvania.
• To compare the pathogenicity of Verticillium species isolated from diseased Ailanthus altissima.

Main Methods:

• Isolation and identification of fungal pathogens from symptomatic Ailanthus altissima.
• Controlled inoculation experiments using Verticillium albo-atrum and Verticillium dahliae on Ailanthus seedlings and canopy trees in greenhouse and field settings.
• Monitoring of disease progression and tree survival rates post-inoculation.

Main Results:

• Verticillium albo-atrum was consistently isolated from highly impacted Ailanthus stands, while V. dahliae was found in less affected areas.
• Both V. albo-atrum and V. dahliae successfully infected Ailanthus altissima under experimental conditions.
• Inoculation with V. albo-atrum resulted in 100% mortality of Ailanthus seedlings and canopy trees within 3 months, demonstrating higher pathogenicity than V. dahliae, which caused mortality in only 16% of inoculated trees after 1 year.

Conclusions:

• Verticillium albo-atrum is identified as the principal causal agent of the Ailanthus wilt epidemic in south-central Pennsylvania forests.
• The findings suggest that V. albo-atrum warrants further investigation as a potential biological control agent for managing invasive Ailanthus altissima populations, pending comprehensive risk assessments.