Movement of Phytophthora ramorum Among Camellia spp. in a

Movement of Phytophthora ramorum Among Camellia spp. in a Nursery Setting
Desareé D. Williams (Dr. Lisa Baird and Dr. Sibdas Ghosh) Shiley Center for Science and Technology, University of San Diego, San Diego, CA 92110; Natural
Sciences and Mathematics, Dominican University of California, San Rafael, CA 94901
INTRODUCTION:
In March 2004, it was announced that Camellias infected with Phytophthora ramorum were discovered at Specialty Plants (San Diego County) and Monrovia Wholesale
Nursery (Los Angeles County). P. ramorum is the causative plant of Sudden Oak Death (SOD) which occurs in tanoaks, oaks, and other susceptible host plants. It is
thought that transfer of the pathogen occurs through direct foliar contact, water splash (from wind, rain, and irrigation), or movement of infected plant material, such as
leaves, stems, and mulch. The purpose of this research project was to observe the spread of Phytophthora ramorum in a nursery setting and reduce its spread through
nursery stock shipments.
METHODOLOGY:
Six plots were set up in a nursery with one gallon pots of Camellias in a
circular array with an infected Rhododendron in the center:
• Each plot had 6 plants (at 0m, 1m, and 2m) from its neighbor and the host
• Additional uninfected plants were kept more than 10 meters away and
served as controls.
Camellias and Rhododendrons in plot 1
The Nursery site:
• Bark and mulch was used for ground cover.
• A fence and canopy were installed to protect the plants from deer, people,
and excessive sun.
• Automatic and drip irrigation systems were installed.
Scanning electron microscope
One of the main aspects of this experiment was to observe the spread of P. ramorum within the nursery site. Due to regulations and restrictions, we were unable to have the
Rhododendrons inoculated with the pathogen at the start of the experiment. Instead we are currently waiting for permit to use the pathogen on-site. However, ten Camellias
were taken to the California Department of Food and Agriculture (CDFA) in Sacramento for infection and used for observations in a laboratory setting.
Possible bacteria
Hyphae
Stomata
Dust
Stomata
Zoospore
Underside of a leaf
RESULTS:
In order to observe the progress of infection, leaves and stems from the camellias were harvested at various intervals from the time of infection. After the Camellias were
infected, they were sent to a lab in the University of San Diego (USD) for microscopic studies. This studies will help better understand how P. ramorum moves through the
Camellias with the aid of electron microscopes. In order observe the progress of infection, leaves and stems from the Camellias were harvested regularly from the time
infection was detected. Light microscopy, transmission (TEM) and scanning electron microscopy (SEM) were used to examine the progression. Light microscopy and SEM
were used to discern pathogen’s method of entrance in the plant. Additionally, they were also used to progression of infection through the leaf and/or stem tissues. TEM will
allow us to determine some of the changes that may occur at the subcellular level.
CONCLUSION:
• SEM pictures show the development and movement of pathogen zoospores and hyphae.
• At this point, only the movements of the pathogen have been observed.
• Currently, it is not completely conclusive how the pathogen enters the plant tissue.
• However, some pictures do show interactions between the camellia stomates and pathogen hyphae.