Semester

Summer

Date of Graduation

2024

Document Type

Thesis

Degree Type

MS

College

Davis College of Agriculture, Natural Resources and Design

Department

Not Listed

Committee Chair

Matthew Kasson

Committee Co-Chair

Brian Lovett

Committee Member

Brian Lovett

Committee Member

Daniel Panaccione

Abstract

Tree-of-heaven (Ailanthus altissima) is a highly invasive tree species with a cosmopolitan distribution, including an expansive range in North America. In the U.S., tree-of-heaven has established populations in more than 40 states and is considered among the most notorious of invasive plant species. The discovery of Verticillium nonalfalfae and V. dahliae causing acute wilt and mortality of Ailanthus in the mid-Atlantic in the 2000s has resulted in numerous studies evaluating the utility of these fungi as potential biocontrol agents. Recent efforts to commercialize V. nonalfalfae have raised additional questions about its widespread use and factors influencing long-term efficacy. Efforts of this study focused on: 1) investigating the ecological interactions of V. nonalfalfae and V. dahliae with mycorrhizal fungi that may influence Verticillium wilt of Ailanthus disease progression; 2) evaluating the temperature constraints of both Verticillium spp. and the resultant impact on disease development; 3) sequencing of Verticillium genomes and the generation of baseline genomic resources to aid in understanding inter-species and intra-species variation; and 4) conducting cross-pathogenicity assays to evaluate host specificity and adaptation. The presence of a pre-existing mutualistic partnership between Ailanthus and arbuscular mycorrhizal fungi (AMF) impacted Verticillium wilt disease development, though the extent to which varied by species and increasing temperatures. Cross-pathogenicity assays revealed that V. nonalfalfae strains were more virulent in their respective hosts of origin than in other known hosts of the fungus, providing further evidence of host adaptation. Sequencing of V. nonalfalfae and V. dahliae genomes confirmed that genes involved in the regulation of mating and putative biosynthetic gene clusters are highly conserved. These genomic resources can be leveraged for the continued investigation of V. nonalfalfae strains being considered for registration, along with V. dahliae strains from Ailanthus that have been historically excluded. Taken together, these results indicate that V. dahliae may serve as an effective biocontrol in the southern U.S., but in-depth host range studies and comparative pathogenicity assays are needed for strains isolated from Ailanthus. In addition, these results suggest that V. nonalfalfae strains isolated from Ailanthus are highly effective and host-specific and, thus, support ongoing efforts to register this fungus as a biocontrol agent against the invasive tree-of-heaven.

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