Investigation of Phytophthora species: Phytophthora colocasiae on Taro and Phytophthora Recovered from Streams in Eastern Tennessee

Oomycetes, also known as water molds, are morphologically similar to fungi. Unlike fungi, they are diploid and more closely related to plants. Several oomycetes are pathogenic to plants as well as aquatic animals. Members of the genus Phytophthora are a threat to many economically important crops and natural forest systems. The research presented in this thesis addresses intraspecific and interspecific variation in natural populations of Phytophthora. Chapter two summarizes genetic diversity and population structure for Phytophthora colocasiae attacking taro in Hawaii, Vietnam and Hainan Island, China based on novel single nucleotide polymorphism (SNP) markers. Phytophthora colocasiae causes Taro Leaf Blight, one of the most important diseases limiting this globally important source of food. Genetic analysis of P. colocasiae recovered from different locations showed that clonal lineages are widely distributed within populations and some clonal lineages are shared between the countries. Chapter three reports species diversity for Phytophthora and Pythium recovered from ten streams in eastern Tennessee in 2010 and 2011. This work is based on a program to monitor natural waterways for the sudden oak death pathogen, P. ramorum; a serious threat for many naturally occurring plants in east Tennessee. Molecular tools were used for identifying species recovered from the streams. During this survey, several known and unknown Phytophthora and Pythium species were identified along with a newly proposed genus Phytopythium.