A third Sudden Oak Death Science (SOD) Symposium was held in Santa Rosa, California in March 2007 to discuss the science surrounding one of the most interesting cases of invasive plant pathogens to date. The causal agent, Phytophthora ramorum, was described in the literature only as recently as 2001, being first documented as causing twig blight of rhododendron in Germany and the Netherlands in the early 1990s and later recognized as being a causal agent of broad-scale Oak declines in the United States. It is a disease of both nurseries and natural woodland ecosystems. Its name may seem misleading  the disease onset is not necessarily sudden as the pathogen infects more than 40 host genera in addition to Oaks, and it does not always cause death. With this in mind it has been important to share knowledge in forums such as the SOD symposiums in order to understand and combat this invasive Phytophthora species which has the ability to affect socio-politics, economics and the structure of natural ecosystems.

As a fresh-faced, enthusiastic PhD student with the CRC at Murdoch University studying Australian Plant Susceptibility to Phytophthora ramorum the symposium was somewhat a ‘baptism of fire'. The symposium was excellent for getting me up to speed in a short amount of time, in helping to build relationships with collaborators in Australia, the UK and the USA, and in formulating the most effective methods and plan of action for my studies. Additionally, while in California I had the opportunity to visit laboratories and field sites to experience the research climate and disease caused by the pathogen first-hand.

The symposium was well organised, with only concurrent sessions on forestry and horticultural needs assessments held on the last day. There was a panel on the first day on specific risk to conifers, with the overall message being positive for the industries and natural ecosystems containing these species. There were updates on wildlands, nursery and regulations. Other symposium topics covered were research on: landscape monitoring and mapping; diagnostics; nursery research and management; forest quarantine issues; biology and ecology; genetics; modelling; and landscape management.

Key presentations were:

Kelly Ivors on a new web-based Phytophthora database which links people to key information regarding a number of Phytophthora species, including host ranges, key papers and molecular sequencing data. Anyone can join up to login, but only key personnel will have access to change or add things to the database, which they hope will result in a well-respected database The website is: www.phytophthoradb.org [1]

Matteo Garbelotto gave a diagnostics presentation on Antonio Chimento's work detecting and quantifying mRNA by reverse transcription real-time PCR as an indicator of viability in P. ramorum infected soil and plant material was super interesting. Basically the idea is that you can detect whether the pathogen is still breathing?, although it may not be active and difficult to culture.

Work presented independently by Kurt Heungens and Steve Tjosvold showed that there are a number of environmental and seasonal factors, as well as host-pathogen interactions pertaining to leaf age and morphology which affect plant susceptibility of plants to P. ramorum. For instance, young leaves were more susceptible when wounded than old leaves, but were less so when not (perhaps due to fine hairs etc on surface preventing zoospore entry) in the work of Heungens and his colleagues.

Additionally, plants infected during the winter months tended to show greater susceptibility than those infected in summer by Tjosvold's group in their mock nursery setting, while the work by Huengens and associates showed great variability in laboratory settings.

Pertaining to biology and ecology, it has been found that P. ramorum is moving in the xylem of infected trees (Anna Brown and Jennifer Parke). Clive Brasier and the Forest Research team?s work on infection of tree stems by zoospores showed a really interesting method of ‘bait log' - out in the field under infected sporulating hosts, while work from a few sources (Steve Tjosvold, Gary Chastagner) showed that flowers and fruit are able to become infected, including mistletoe inflorescences which can be spread into uninfected stands of trees by breaking off. Sandra Denman's work on sporulation of P. ramorum and P. kernoviae on asymptomatic foliage and fruit was really interesting, and concerning.

Research into the genetics of P. ramorum should prove to be a burgeoning field in future, especially given that the entire genome has been mapped, along with genomes of P. sojae and P. infestans, which offers opportunities for comparison amongst species.

Following the symposium I visited the University of California Davis and UC Berkeley laboratories, headed by Dave Rizzo and Matteo Garbelotto respectively, saw the disease first-hand at Steve Tjosvold's (UC Extension) mock nursery site in Santa Cruz. I also made contact with Holly Forbes of the UC Berkeley botanical gardens.

Overall, this trip has made me more aware of the increasingly socio-political and economically driven environment that researchers of biosecurity threats operate within. Clive Brasier presented an interesting talk on P. ramorum and P. kernoviae as international biosecurity failures, cautioning on the movement of plants (and pathogens) throughout the world. When dealing with these issues it is important to communicate effectively to the public, the politicians and the policy makers the importance of sound science in making effective pre-emptive management decisions for invasive organisms.

Information on SOD and the program of events of the symposium can be found at: http://www.suddenoakdeath.org/ [2]

Location