Phytophthora ramorum, the causal agent of sudden oak death, is a threat to the Gulf Coast region. There is a concern that infected nursery stocks can move to the Eastern United States through nursery trade. Three different studies focused on P. ramorum examined the susceptibility of select Gulf Coast forest species, the direct effects of salinity on the pathogen, and monitoring South Louisiana waterways using stream baiting techniques. The only study not conducted at the USDA-ARS, Foreign Disease Weed Science Research Unit (Fort Detrick, Maryland) was stream baiting for P. ramorum in South Louisiana.
The study for screening Gulf Coast forest species examined the reaction of several plant species native to the Gulf Coast forest when inoculated with P. ramorum. These species included yaupon (Ilex vomitoria ), spice bush (Lindera benzoin), Southern magnolia (Magnolia grandiflora), sweetbay magnolia (Magnolia virginiana), black willow (Salix nigra), baldcypress (Taxodium distichum), Virginia creeper (Parthenocissus quinquefolia) from two genotypes (Louisiana and Maryland), and Eastern baccharis (Baccharis halmifolia). Significant differences (P<0.05) in the percentage of necrosis of the leaves between inoculated and non-inoculated control plants were found on yaupon (P=0.0008), Southern magnolia (P=0.001), and sweetbay magnolia (P=0.0009). In addition, Virginia creeper, although did not display visible symptoms, did become infected with P. ramorum. Yaupon and Virginia creeper may be new susceptible hosts to P. ramorum. An expanded understanding of the susceptibility of Gulf Coast understory species and the knowledge of new susceptible species can be used to develop a management plan if the pathogen becomes established in Gulf Coast region.
Research on the effects of salinity on P. ramorum viability and infectivity was to gain an understanding of the effect of different salinity levels on the infectivity of P. ramorum. This pathogenic species has been found in waterways outside the boundaries of infested ornamental nurseries outside of California and Oregon. Very little is known about what factors are conducive to its survival and sporulation in water. Water naturally collected from various sources and different saline levels created under laboratory conditions was used to better understand what effect salinity has on the life cycle of P. ramorum and its ability to infect tissue. The research demonstrates that P. ramorum can form infective propagules at high salt concentrations that can infect plant tissue gaining an insight as to the survival and factors affecting infectivity of P. ramorum.
Stream baiting in South Louisiana for P. ramorum consisted of five different waterways, which included the Amite River, Mississippi River, Lake Pontchartrain, Atchafalaya Basin, and Southern Ravine. The waterway locations were distributed across four different Parishes (Counties) and represented different ecosystems. Floating mesh bags containing whole Rhododendron 'Cunningham's White' leaves were used to monitor in each location from December 2010 to January 2011. Phytophthora ramorum was never recovered during the survey. However, a total of 34 positively identified cultures, encompassing 10 different Phytophthora and Pythium species, were identified using ITS PCR molecular techniques at the USDA-ARS Genetic Improvement of Fruits & Vegetable Laboratory Beltsville Agricultural Research Center (Beltsville, MD). Oomycetes species in Louisiana waterways will add to other national survey results that provide information as to the distribution of these species. This will greatly assist management strategies before P. ramorum and other Oomycetes become established permanently in a natural ecosystem.
|Advisor:||Collins, Daniel J.|
|Commitee:||Ghebreiyessus, Yemane, Qi, Yadong, Widmer, Timothy L.|
|School:||Southern University and Agricultural and Mechanical College|
|School Location:||United States -- Louisiana|
|Source:||DAI-B 73/03, Dissertation Abstracts International|
|Subjects:||Urban Forestry, Plant Pathology|
|Keywords:||Gulf Coast, Phytophthora ramorum, Salinity, Stream baiting, Sudden oak death|
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