Molecular Analysis and Thermal Treatment of Several Phytophthora Species Causing Diseases of Ornamental Plants in California.

The genus Phytophthora encompasses a range of fungal pathogens infecting and killing ornamental plant species. P. ramorum, is known to be the causal agent of “Sudden Oak Death” (SOD), a disease that currently plagues Oak forests of coastal California and Oregon. Able to spread through water and trade of poorly monitored ornamental plants, the various strains of Phytophthora can spread rapidly unnoticed. Currently no known treatments efficiently terminate the spread of SOD in forests. Other Phytophthora species such as P. fallax, P. syringe, and P. tentaculata, have been observed recently in nurseries causing symptoms which mimic P. ramorum. To better understand the facets that govern the spread of Phytophthora, researchers at the National Ornamentals Research Site at Dominican University (NORS-DUC) analyzed and developed various techniques to control the proliferation and spread of this pathogen. Results from past experiments have demonstrated that P. ramorum can be neutralized through the use of high-temperature soil steaming. In this battery of experiments, we tested the effects of both wet and dry heat at temperatures of 30°C, 40°C, 50°C, 60°C, for 30, 60, and 120 minutes on isolate strains P. fallax, P. syringe, and P. tentaculata in the lab. Post-steamed samples were plated on selective media to test for survival rates. In addition, a steaming experiment was performed at the NORS-DUC nursery. The inoculum was placed at soil depths of 5cm, 15cm, and 30cm, and steamed for neutralization. Analysis of the Phytophthora phylogeny would contribute to molecular species identification and understanding of the genetic traits leading to symptom development. Phylogenetic relationships of the nursery pathogens were studied using sequence information of ITS, β-tubulin, elongation factor 1 α, and cytochrome oxidase I and II. The markers were evaluated through PCR and sequence analyses, followed by phylogenetic tree construction using the distance based neighbor-joining method with BLAST2 and ClustalW programs. With this research, we hope to identify and develop a safe, simplistic, and more efficient way of protecting native plants against P. ramorum and other plant pathogens.