Posts Tagged: Matteo Garbelotto
In 2014, plant biologists with the California Department of Agriculture reported an alarming discovery: native wildflowers and herbs, grown in nurseries and then planted in ecological restoration sites around California, were infected with Phytophthora tentaculata, a deadly exotic plant pathogen that causes root and stem rot.
While ecologists have long been wary of exotic plant pathogens borne on imported ornamental plants, this was the first time in California that these microorganisms had been found in native plants used in restoration efforts. Their presence in restoration sites raised the frightening possibility that ecological restoration, rather than returning disturbed sites to their natural beauty, may actually be introducing deadly plant pathogens, such as those related to Sudden Oak Death, into the wild.
New work by a UC Berkeley team in the College of Natural Resources shows for the first time just how widespread and deadly the threat of pathogens from restoration nurseries may be.
The team surveyed five native plant nurseries in Northern California and found that four harbored exotic, or non-native, Phytophthora pathogens. Strains of the pathogens from native plant nurseries were shown to be at times more aggressive than strains found in the wild, and some of them are rapidly developing resistance to the fungicides that can be used to control them, the researchers found.
Working with restoration nurseries around the state, the researchers showed that new management techniques, coupled with new methods for detecting pathogens, can help these nurseries limit the spread of exotic pathogens.
"Some of these restoration projects cost tens of millions of dollars, but of course their actual value is much higher, because of the wealth of services healthy natural ecosystems provide, including supporting animal and plant biodiversity, providing good water and air quality, and enjoyable recreation sites," said Matteo Garbelotto, UC Cooperative Extension specialist and adjunct professor of environmental science, policy and management at UC Berkeley.
"Such services are highly diminished in ecosystems affected by exotic plant diseases, while water runoff and erosion, the establishment of exotic plants and animals, and even hotter wildfires may increase in conjunction with disease outbreaks in natural ecosystems," Garbelotto said.
Pathogens evolve to outwit fungicides
Bacteria that make humans sick are constantly evolving to resist the antibiotics designed to fight them, and resistance to fungicides has been documented in microbes causing diseases in agricultural plants. Garbelotto and his team wanted to know if the widespread use of fungicides in in native and ornamental plant nurseries could also accelerate the development of fungicide-resistance in plant pathogens.
Their research was spurred in part by their discovery of a new strain of the Sudden Oak Death pathogen in Oregon forests that is highly tolerant of a fungicide commonly known as phosphite, one of the main weapons used against plant parasites in the wild because its application does not cause any known negative environmental side effects.
Together with a group of New Zealand researchers, they decided to study fungicide resistance of Phytophthora -- a genus of plant pathogens that can case lethal cankers and root rot -- to two important fungicides, including phosphite.
The researchers gathered numerous samples of Phytophthora from 11 species present both in forests and plant nurseries. They then tested the sensitivity to phosphite of multiple individuals per species.
While most of the species tested were overall still sensitive to phosphite, strains of four species were able to resist the effects of the chemical, the researchers report in PLOS ONE. These include Phytophthora ramorum, the parasite behind Sudden Oak Death in North America and Sudden Larch Death in Europe, and Phytophthora crassamura, a species first discovered recently by the same UC Berkeley researchers in native plant nurseries and restoration sites in California.
Some strains within each of these four species, although genetically almost identical to strains still susceptible to phosphite, were resistant to it. The presence of chemical tolerance or chemical sensitivity when comparing nearly genetically identical strains suggests that the development of resistance occurred relatively recently, perhaps in response to the widespread use of phosphites in native and ornamental nurseries, Garbelotto said.
"These pathogens can be literally flooded with these chemicals in plant production facilities, and at the beginning of the study, we hypothesized that in such predicaments these pathogens would be forced to evolve resistance" Garbelotto said. "Indeed, our hypothesis was correct, and we found that some of them evolved the ability to tolerate exposure to phosphite."
While phosphite can still help to spur a plant's immune system, this may not be enough to quell the spread of the disease, Garbelotto said.
"By pressuring these pathogens to evolve resistance to phosphites, we are effectively taking out phosphite as a potential tool to manage these disease outbreaks," Garbelotto said. "Furthermore, the ability to quickly develop tolerance to a fungicide may be an indication these pathogens can adapt quickly to new environments. Thus, they may become formidable invasive organisms, infesting larger swaths of natural areas and causing significant disease and mortality of essential native flora."
A widespread - but reparable - problem.
Since the first discovery of Phytophthora in California restoration sites, research by the UC Berkeley team and others have traced the deaths of wild trees and plants back to strains of the pathogen originating in native plant nurseries, rather than strains already found in the wild. However, few studies have documented just how prevalent the problem is.
In a recent study published in the journal Plant Pathology, UC Berkeley researchers examined 203 individual plants across five restoration nurseries in California and found that 55 of the plants were infected with Phytophthora.
"We were able to prove that this is a widespread problem in California," Garbelotto said. "Most of the stock that they used is infested, and the levels were very high. For some species more than 50 percent of the plants we tested were infected."
The team then worked with the infected nurseries to implement new best management practices to try to limit the spread of disease without the use of phosphite or of other fungicides. These simple guidelines, which included more careful management of water runoff and soil to reduce cross contamination, reduced the prevalence of disease to nearly zero a year after implementation.
"We were able to prove that after a year of following the guidelines, those facilities were clear of pathogens, and other facilities that did not follow the guidelines still had the pathogens," Garbelotto said. "As a result of these findings, people are now putting a lot of money and effort into making sure that the plants are clean, by following similar guidelines and by making sure that no fungicides are used to avoid the development of resistance."
Co-authors on the PLOS ONE study are Shannon Hunter of the University of Waikato in New Zealand and Nari Williams, Rebecca McDougal and Peter Scott of Forest Protection in New Zealand. Co-authors on the Plant Pathology study are L. Sims of UC Berkeley and S. Tjosvold and D. Chambers of the University of California Cooperative Extension.
This research was supported by the Endemic and Invasive Pests and Diseases Strategic Initiative of the University of California, Agriculture and Natural Resources; and by the San Francisco Public Utilities Commission in collaboration with the U.S. Forest Service (Region 5).
Overall, 3.5 percent of the trees (based on those areas sampled during the blitzes) were found to be P. ramorum positive, a threefold drop from 2017. Yet, in San Mateo, Santa Clara and Santa Cruz counties, infection levels were estimated to be as high as 19 percent, followed by 12.7 percent in the East Bay.
"Oaks and tanoaks were infected last year and will be showing symptoms such as bleeding in the stem and canopy drying this year and in the next two years to follow. Hence, despite a reduction of SOD infection on leaves of California bay laurels and leaves of tanoaks in 2018, we can expect a sharp increase in oak and tanoak mortality in 2018, 2019 and 2020."
Notable outbreaks were detected in Alameda (El Cerrito and Oakland urban parks, San Leandro, Orinda, Moraga), Marin (Novato, Day Island, Woodacre, Sleepy Hollow, McNears Beach, China Camp State Park, north San Rafael, Tiburon Peninsula, east and west peak of Mt. Tamalpais, Marin City), Mendocino (south of Yorkville), Monterey (Carmel Valley Village, Salmon Creek Trail in southern Big Sur), Napa (east Napa city), San Mateo (Burlingame Hills, west of Emerald Hills and south of Edgewood Rd, Woodside ), Santa Clara (Los Altos Hills, Saratoga, Los Gatos, along Santa Cruz Co border), Santa Cruz (along the Santa Clara Co border, Boulder Creek), and Sonoma (near Cloverdale, east and west of Healdsburg, west of Windsor, east of Santa Rosa, west of Petaluma) counties.
Several popular destinations where P. ramorum was found positive during the 2017 Blitz were negative for the pathogen in 2018, including Golden Gate Park and the Presidio of San Francisco, the UC Berkeley campus, and Mount Diablo State Park. Samples from San Luis Obispo and Siskiyou counties were also pathogen-free as were those from the southern portion of Alameda County.
“It is encouraging that SOD has yet to be found in the forests of California's northern-most counties, San Luis Obispo County and southern Alameda County,” said Garbelotto.
“It is also encouraging to see that despite its continued presence in the state for more than 20 years, SOD infection rates drop during drier years,” he said. “However, in 2018, we identified a number of communities across several counties where significant outbreaks were detected for the first time, and the Salmon Creek find in Monterey County is the southernmost positive WUI (wildland-urban interface) tree detection ever. Until the 2018 Blitz, only stream water had been found positive in the Salmon Creek area. We encourage everyone in affected counties to look at the Blitz results online and to attend one of the fall workshops to learn how to protect their oaks from SOD.”
Citizen-science SOD Blitz workshops
SOD Blitz Workshops are being held this fall in Santa Rosa (Oct. 10), Portola Valley (Oct. 16) and Berkeley (Oct. 17). The trainings will discuss Blitz results and recommendations for protecting oaks in the WUI. Workshops are intended for the general public, tree care professionals and land managers (see www.sodblitz.org for details). Two International Society of Arboriculture continuing education units will be offered at each training. Data collected from the Blitz (both positive and negative samples) have been uploaded to the SOD Blitz map (www.sodblitz.org ) as well as to SODmap (www.SODmap.org) and to the free SODmap mobile app, which can serve as an informative management tool for people in impacted communities.
Twenty-five SOD Blitz surveys were held in 2018 in the WUI of 14 coastal California counties from the Oregon border to San Luis Obispo County and included three tribal land surveys. The 304 volunteers surveyed approximately 13,500 trees and submitted leaf samples from over 2,000 symptomatic trees to the Garbelotto lab for pathogen testing.
SOD Blitzes are a citizen science program, which train participants each spring to identify symptomatic tanoak and California bay laurel trees in the WUI and to properly collect samples in the interest of generating an informative map of P. ramorum disease symptoms over time. Samples are tested for the presence of the pathogen at UC Berkeley and results are posted electronically each fall. Now in its eleventh year, the SOD Blitz program is one of the first in the world to join researchers and volunteers in a survey for a tree disease.
SOD Blitz surveys were made possible thanks to funding from the US Forest Service State and Private Forestry, Midpeninsula Regional Open Space District, and the PG&E Foundation. The Blitzes were organized by the UC Berkeley Garbelotto lab in collaboration with the National Park Service, Presidio Trust, San Francisco Public Utilities Commission, Midpeninsula Regional Open Space District, Save Mount Diablo, Land Trust of Santa Cruz County, East Bay Regional Park District, Santa Lucia Conservancy, Sonoma State University, UC Santa Cruz Arboretum, Los Padres National Forest, City and County of San Francisco Department of Recreation and Parks, UC Berkeley Botanical Garden, and California Native Plant Society.
For information on the status of P. ramorum/SOD tree mortality in California wildlands, see the US Forest Service 2018 Aerial Detection Survey results at https://www.fs.usda.gov/detail/r5/forest-grasslandhealth/?cid=fseprd592767.
For more information on the SOD Blitzes, visit www.sodblitz.org or contact Katie Harrell at (510) 847-5482 or email@example.com. For more information on Sudden Oak Death and P. ramorum, visit the California Oak Mortality Task Force website at www.suddenoakdeath.org or contact Harrell.
Results of the 2015 Sudden Oak Death Blitz survey reveal coastal mountain infestations in areas such as Big Sur (19% infection), the Santa Cruz Mountains (13% infection), and western Sonoma County (12% infection) remain high despite an overall decline in infection rates from 4.4% to 3.7% across California's 15 infested counties.
Sudden oak death (SOD) symptoms have been seen in Alameda, Contra Costa, Humboldt, Lake, Marin, Mendocino, Monterey, Napa, San Francisco, San Mateo, Santa Clara, Santa Cruz, Solano, Sonoma and Trinity counties.
“Understanding the current disease distribution is key to preventing sudden oak death spread. Citizen scientists have been an invaluable help with this task over the last decade,” said Matteo Garbelotto, UC ANR Cooperative Extension specialist in the Department of Environmental Science, Policy and Management at UC Berkeley, who organizes the annual SOD Blitz.
Several new SOD outbreaks of note were identified during the blitzes. Two infected California bay laurel trees were confirmed near UC Berkeley's West Gate, a high-traffic, high-risk area with many heritage oaks. An infected California lilac shrub was found in the Presidio of San Francisco's (part of the Golden Gate National Recreation Area) southeastern quadrant. An infected California bay laurel tree was confirmed in Danville (eastern Contra Costa County) in an area where SOD had not previously been reported, and an urban park in Saratoga was found infested for the first time.
Nineteen citizen science-based SOD Blitzes (largest number of blitzes to date) were held this spring, two of which were new this year – one in Trinity County and one on Kashia Band of Pomo Indian land in Mendocino County. The 504 volunteers surveyed nearly 10,000 trees from San Luis Obispo County, north to Mendocino and Trinity counties. Each volunteer was trained to identify Phytophthora ramorum (the plant pathogen known to cause SOD) symptoms on California bay laurel and tanoak leaves. “Blitzers” had up to three days to collect and record locations of symptomatic samples, which were then sent to the Garbelotto lab for DNA analysis to determine the presence or absence of the pathogen.
Garbelotto is sharing results from the spring blitzes as well as new recommendations for SOD management at workshops being held around the Bay Area. Workshops will be held in Sebastopol on Nov. 3, in Berkeley on Nov. 4, and in San Rafael on Nov. 13. For details, see “Community meetings” at sodblitz.org.
For landowners in infested areas concerned about protecting their oak trees, Garbelotto will reveal his updated three-step SOD management plan. He will show them how to:
- Use the SODMap mobile app to help assess risk of oak infection (see sodmapmobile.org).
- Determine if California bay laurel trees near high-value oaks should be considered for removal (using a new buffer zone new chart - http://nature.berkeley.edu/garbelottowp/?page_id=2345).
- Apply phosphonates to high-value oak and tanoak trees to boost immunity (updated dosages and application frequencies at http://nature.berkeley.edu/garbelottowp/?page_id=2348).
Infection on California bay laurel and tanoak leaves indicates arrival of P. ramorum to an area, but true oak (California black oak, coast live oak, canyon live oak and Shreve's oak) infection typically requires a couple of years with wet conditions after pathogen arrival. Therefore, preventatively treating oaks to help ward off infection is best done when early indicator species first show symptoms, prior to oak infection and optimal conditions for the pathogen – cool and moist.
These surveys are made possible thanks to funding from the USDA Forest Service and the PG&E Foundation as well as help from the California Native Plant Society.
For more information on the workshops, go to sodblitz.org or contact Katie Harrell at (510) 847-5482 or firstname.lastname@example.org. For more information on sudden oak death and P. ramorum, visit the California Oak Mortality Task Force website at suddenoakdeath.org.
UC, federal and state agencies and landowners in Humboldt County recently received national recognition for their collaborative efforts to halt the spread of sudden oak death. Kathleen Merrigan, U.S. Department of Agriculture deputy secretary, praised the partnership during her visit to Davis on May 16.
Yana Valachovic, UC Cooperative Extension advisor in Humboldt County, and Dave Rizzo, professor in the Department of Plant Pathology at UC Davis, were joined at the USDA offices in Davis by their partners from USDA Forest Service, CAL FIRE and the Natural Resources Conservation Service to accept the Two Chiefs’ Partnership Award. Merrigan presented the award on behalf of the “two chiefs” – the head of NRCS and the head of the Forest Service.
For me, it was a pleasure not just to see Yana’s efforts rewarded, but also to see Dave Rizzo. About a decade has passed since the days I was on the phone and email almost daily forwarding reporter requests for interviews to the UC Davis plant pathologist. Rizzo was first to identify Phytophthera ramorum as the pathogen that causes sudden oak death in 2000.
Although SOD doesn't make the news as frequently as it did in the early 2000s, it continues to spread. Garbelotto’s "SOD Blitz," his annual survey, found in 2011 that the rate of infection in trees between Napa and Carmel had grown as much as three times the rate of the previous year.
Since the disease was first reported in Marin County in 1995, it has been found in 14 coastal California counties and killed over 5 million tanoak, coast live oak, California black oak, Shreve oak and canyon live oak trees, according to the Forest Service.
UC Cooperative Extension employees were surprised in the spring of 2010 when routine monitoring near the mouth of Redwood Creek in Humboldt County detected P. ramorum in leaf samples. It meant that trees were infected somewhere in the 200,000-acre watershed – more than 50 miles from the nearest known infestation and farther north than the pathogen had ever been detected in California.
UCCE staff coordinated a swift management response, embarking on the largest SOD management project ever to occur in California. They collaborated with the Forest Service, NRCS, CAL FIRE, tribes, local timber companies and private landowners to remove infected plant material. Rizzo pitched in with diagnostics for the project and matching funds to qualify for a federal grant.
It’s still not clear how the pathogen got to Redwood Valley, said Valachovic, but it could threaten the dense tanoak forests of the surrounding area, killing trees and leaving behind dry brush, which could fuel wildfire.
Landowner support has been critical to the success of the project, according to Valachovic. More than 20 landowners in the valley have allowed monitoring and treatment activities on their properties, recognizing that their cooperation may keep the disease from spreading to other areas.
The first phase of treatment is currently wrapping up, and UCCE is beginning to monitor project efficacy and watch for spread of the pathogen beyond project boundaries. The Yurok and Hoopa tribes will be paying close attention to this effort, as they are only a ridge away from the infestation.
“Oaks are an important part of our culture and history, and we will do what we can to keep sudden oak death out of our forests,” says Ron Reed, a Yurok tribal forester.
OakMapper website. The website also features a map showing suspected and confirmed cases of sudden oak death.
Scientists, managers, regulators and policymakers will gather June 19-22, 2012, to discuss the latest news about the disease at the Fifth Sudden Oak Death Science Symposium in Petaluma.
For more information about sudden oak death disease, visit the California Oak Mortality Task Force website at www.suddenoakdeath.org.