Doctoral Dissertations

Date of Award

5-2008

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Plants, Soils, and Insects

Major Professor

Kurt H. Lamour

Committee Members

Bonnie H. Ownley, J. Kevin Moulton, W. Hayes McDonald, Mark T. Windham

Abstract

Molecular and morphological characterization of Phytopthora isolates recovered from Ericaceous nursery hosts throughout the state of Tennessee over two years allowed for the identification of six known species and one previously undescribed species. The undescribed species was observed in California and Tennessee simultaneously and a species description is provided for P. foliorum sp. nov. Of the six known species recovered from nursery hosts, P. citricola and P. citrophthora were recovered most frequently, exhibit diverse AFLP genotypes within the state, and are likely moved via the nursery trade. Other species recovered included P. cactorum, P. nicotianae, P. palmivora, and P. tropicalis. Upon the observation of both P. tropicalis from nursery hosts and P. capsici from vegetable hosts within the state interspecific crosses were performed between isolates from each species. Characterization of oospore progeny using AFLP and DNA sequence data from these crosses demonstrate that interspecific hybridization is possible. Additionally, apomixis or asexual reproduction via a sexual structure was observed in some crosses. Utility of AFLP markers used in these crosses quickly degraded. Upon these observations, a novel set of DNA-based markers were sought for use with laboratory crosses and field isolates. Using primary sequence data from the P. capsici genome sequencing project 36 loci were analyzed in a four isolate panel, plus one isolate of P. tropicalis. A subset of assays were developed using high-resolution DNA melting analysis. These assays were implemented in characterizing field isolates from one vegetable production facility over four years. The data suggests that the sexual stage and recomnbination is occurring in Tennessee vegetable fields infested with P. capsici.

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