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Berkeley, California, USA
19th – 25th June 2022
The University of California, Berkeley, hosted the meeting, and for many of us it was our first overseas travel since March 2020, with preparations conducted under some apprehension due to the ongoing maze of Covid regulations and the threat of random flight cancellations. The relaxation of the USA’s requirement for a pre-departure videoed LFT one week prior to my departure was a welcome development and happily my travel to San Francisco was smooth.
I arrived two days before the conference began; buffer time in case of travel disruption, and after a day of walking 20+ km around this wonderfully dramatic city with its extreme and rather unsettling contrasts between rich and poor, I spent a day with Tyler Bourret from the University of California, Davis. Tyler and I share interests in the risks of unintentional Phytophthora introductions into native landscapes via restoration plantings and risk mitigation through nursery best practice. Tyler was a superb host, and we visited some native plant restoration sites in Presidio Park as well as one of the local native plant nurseries which was a shining example of immaculate practice!
The meeting began the next day with a trip across the Golden Gate Bridge to visit old growth coastal redwoods and discuss the devastating ecological impacts on native broadleaves of the invasive forest pathogen Phytophthora ramorum. This was followed by a trip to a coastal scrub restoration site where Phytophthora had been detected in new plantings. After that we travelled inland to see P. ramorum killing coast live oaks and discuss Phytophthora-wildfire interactions; forest fires of course being a hugely topical issue in California currently. The field tour ended with pizza and beer, and we were brought to the University of Berkeley campus where the main conference started with a plenary address ‘Meeting the challenges of Phytophthora diagnostics in California’ by Suzanne Latham of the California Department of Food and Agriculture with whom I collaborate in an international project looking at spread of Phytophthora in plant nurseries.
Conference sessions during the week were themed around forest Phytophthora diagnostics, diversity, epidemiology, host-pathogen-environment interactions and management, with several talks around the topic of control of Phytophthora through nursery best practice and the application of metabarcoding to understand Phytophthora diversity in nurseries and wider environments. Talks generated discussion around topics such as ‘why are there so often discrepancies between baiting and metabarcoding methods for detecting Phytophthora? and the intangibility of persuading Phytophthora to release zoospores – an area where science meets the mystical. One notable talk was by Richard Hamelin of University of British Columbia who reported the worrying discovery of novel and viable intra- and inter lineage hybrid variants of the highly adaptable P. ramorum. Another reason to contain the further spread of this pathogen in trade.
A second field trip mid-week took us to the foothills of the Sierra Nevada range, a desiccated landscape in the grip of the current ‘mega drought’ afflicting California. Here, we saw the startling devastation of rare Manzanita and associated scrub vegetation caused by Phytophthora cinnamomi. We were treated to a somewhat surreal demonstration of Ultra Low Volume Phosphite application using homemade bicycle-driven and hand-held custom spray rigs (the latter brought to mind the ‘cloudbusting’ machine) designed by pathologists come engineers Ted Swiecki and Elizabeth Bernhardt of Phytosphere Research. I am not myself convinced that indiscriminate Phosphite application has a place in native vegetation management, but it was an insight into the brilliant inventiveness of Ted and Elizabeth.
Ted Swiecki demonstrating the bicycle-driven phosphite spray rig for control of Phytophthora cinnamomi killing of native Manzanita in California.
I presented twice, one a short talk on investigating natural resistance in juniper and larch to invasive Phytophthora species and a keynote address on ‘Understanding drivers of Phytophthora emergence through the plant nursery trade in Britain’. For the latter I was given the last 9am slot of the week and am highly grateful for an almost-full house despite the previous night’s 3am finish to the sampling of Berkeley Bars by pretty much everyone else except me. Overall, it was a highly successful meeting and a big thanks to organisers Matteo Garbelotto and Doug Schmidt and their assistants for persevering with this meeting over the last two years despite the many Covid uncertainties. It was wonderful to meet colleagues and collaborators again and to gain insights into the latest in forest Phytophthora research from around the globe.
Sarah Green
The Phytophthora IUFRO meetings are one of the most interesting and helpful conferences for people working on Phytophthora research, as they bring together researchers from different continents to discuss research developments and challenges in the field. My first time at a Phytophthora IUFRO meeting was during 2019 in Sardinia (again BSPP funded), which inspired me to develop an idea about a research project for the RHS. Knowing that the group will be meeting again this year, I really wanted to attend in order to share my thoughts about the project, my struggles during experimental work and most importantly discuss with Phytophthora researchers about how the project can be improved and how we can work collaboratively on an international scale. With no hesitation, I can say that, it was one of the best conferences I have ever attended. The talks covered a huge area of Phytophthora research, from laboratory methodology to management of the pathogen in natural environments. Some topics, which I found particularly interesting, was firstly the relationship between different Phytophthora ramorum hosts (the pathogen has two types of host: dead-end hosts and transmissive hosts) and the impact to Sudden Oak Death spread in California forests. Secondly, the association between wild fires and Phytophthora in forests: how the infections affect the ‘fuel’ for the fires and consequently, how we can manage fires and restore sites.
Further, as I have been struggling with the question, which is the most suitable method to isolate and identify Phytophthora spp. from my samples, I found particularly interesting and helpful the discussion on how we should implement different techniques e.g. traditional baiting methods -sequencing with metabarcoding in order to understand better the diversity of Phytophthora spp. Moreover, the presentations and the follow up discussion, on the huge role that plant trade and nurseries have on Phytophthora spread, was important to help me raise the need to understand the role of gardens within the spread pathways. This assisted me to open the discussion about the RHS work and develop better the project aims. I have been very grateful for the positive feedback, suggestions and support I received from the colleagues in the meeting. I feel extremely privileged that people were happy to collaborate with me and the RHS and make the conference feel inclusive to young researchers.
I believe that in biological research, is crucial to be able to see and understand what is happening outside the lab. This conference had two days of field trips in a diverse range of locations. Probably everyone in plant pathology, knows that P. ramorum is the No. 1 pathogen in forest pathology in California, which puts at risk more than 1.8 billion trees. During the field trip we got the chance to see the impact of P. ramorum in forest sites, how these are managed and the restoration approaches currently used. Also, we had the chance to see sites with P. cinnamomi and discuss the work to understand its introduction to wildlands and the role of different native plants to its spread.
The impact of Phytophthora cinnamomi on wildland during the second field trip.
I cannot close this report without mentioning the beauty of California; The blue skies, the parks, the art-deco architecture of San Francisco combined with the Victorian houses and the music associations of Haight- Ashbury, as well as the UC Berkley (where we were based) created a beautiful environment to relax after the daily sessions. However, most importantly the conference would not be the same without all these lovely and friendly colleagues, who made it such a special experience. I look forward to meeting them all again at the next meeting!
Fryni Drizou
The Royal Horticultural Society, UK
