Semester of Graduation



Master of Science (MS)


Plant Pathology and Crop Physiology

Document Type



Three Oomycetes genera, Phytophthora, Phytopythium and Pythium, contain many important plant pathogens. Historically, Phytophthora infestans, responsible for the great Irish potato famine, and Phytophthora ramorum, causal agent of sudden oak death disease, are the two better-known high impact pathogens. The LSU AgCenter Plant Diagnostic Center (PDC) has been isolating putative Phytophthora and related species from combined root and soil samples collected from various woody ornamentals and trees for over a decade. In August of 2016, Louisiana received torrential rains, which resulted in historic flooding in several southern parishes. During subsequent years, the PDC staff isolated a higher number of putative Phytophthora and related species from woody ornamentals and trees including live oak. The goal of this research was to identify and determine the prevalence of Phytophthora spp. and related genera in the PDC collection using molecular techniques. For this purpose, the internal transcribed spacer region (ITS5 and ITS4) and cytochrome oxidase 1 (COX1F and COX1R) primers were used to amplify targeted DNA from these isolates using a conventional polymerase chain reaction (PCR). The PCR products were sequenced, and the identifications based on the sequence data indicated a diverse group of genera and species. The results suggested multiple possible, unreported host species associations, including some with live oak (Quercus virginiana). Many live oak trees on the LSU campus exhibit decline symptoms. To investigate the potential association of Oomycetes in this decline, a survey of live oak trees on LSU Campus in Baton Rouge was conducted. The sampling resulted in the isolation of Phytopythium vexans from 54% of the soil samples taken from under the trees, whereas Phytophthora spp. were only isolated from 4% of the samples. This research has revealed the prevalence of diverse Oomycetes associated with woody hosts in Louisiana and suggested new, unreported Phytophthora, Phytopythium, and Pythium spp. associations with multiple woody ornamental and trees. Future research, including pathogenicity tests to investigate the possible pathogenic nature of these new host-species associations, may yield information on the importance of the various Oomycetes affecting different woody hosts in Louisiana.



Committee Chair

Singh, Raghuwinder