Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Gene sleuths trace tree-killing pathogen back to California

Genetic detective work by an international group of researchers may have solved a decades-long mystery of the source of a devastating tree-killing fungus that has hit six of the world’s seven continents.

In a study published today (Thursday, Sept. 1) in the peer-reviewed journal Phytopathology, California emerged as the top suspect for the pathogen, Seiridium cardinale, that is the cause of cypress canker disease.

It was in California’s San Joaquin Valley in 1928 that S. cardinale was first identified as the culprit causing the disease. The fungus has made its way since to Europe, Asia, New Zealand, Australia, South America and Africa. In many regions, the pathogen has infected and killed up to 95 percent of native trees in the cypress family, including junipers and some cedars.

“The fungus was likely introduced from California either in the South of France or in Central Italy 60 to 80 years ago, and that introduction resulted in a global pandemic that has devastated the region’s iconic Italian cypress trees,” said Matteo Garbelotto, adjunct associate professor and cooperative extension specialist in ecosystem sciences at the University of California, Berkeley.

The fungus kills a tree by entering through cracks in its bark, producing toxins that wreak havoc with its flow of sap and choke off its supply of water and nutrients. The disease has left an indelible mark throughout Southern Europe.

“Italian cypress trees are important to the ecosystem, but they are also considered the quintessential trees of the Mediterranean, the ones that dot the Tuscan countryside and that form the landscape of much of Greece, the South of France and Spain,” said study lead author Gianni Della Rocca, researcher at the National Research Council in Florence, Italy. “It is difficult to put a price tag on the impact this pathogen has had. It’s hard to imagine the Tuscan or Provence landscape without cypresses.”

DNA detectives

The relatively sudden appearance and destructiveness of the disease in Europe pointed to an exotic pathogen, but scientists didn’t know where it came from. Tracing the origins of the pathogen back to California took some genetic sleuthing by Garbelotto, Della Rocca and their colleagues Catherine Eyre, a UC Berkeley post-doctoral researcher in ecosystem sciences, and Roberto Danti, a researcher at the Italian National Research Council.

The researchers used modern DNA fingerprinting techniques to analyze 96 S. cardinale isolates of diseased tree samples from seven Mediterranean countries, eight California counties, Chile and New Zealand.

S. cardinale is capable of reproducing asexually by creating genetically identical clones of itself, or sexually when a different variant is available for mating.

California emerged as a likely culprit because it hosts populations of the pathogen that are genetically diverse, a strong sign that the pathogen is endemic to the region, the researchers said. The study authors attribute the diversity to the likely sexual reproduction of two genetic variants of the pathogen found in California.

In contrast, the researchers found that one of the two variants of S. cardinale endemic to California is responsible for the epidemic of cypress canker in the Mediterranean, an indication that the fungi there all descended from a “founder” genotype that made its way to Europe.

The second variant found in California, incidentally, has been linked to the epidemic in countries in the Southern Hemisphere such as New Zealand and Chile.

Just how the pathogen moved from California outward is not yet clear, the researchers said. What they can say with certainty is that humans helped the pathogen along in its journey, since air and sea currents alone could not account for the discovery of identical genotypes thousands of miles apart. The paper reports that strains of the pathogen with identical DNA profiles were found hundreds to thousands of miles apart, an indication that humans are actually moving the pathogen, most likely thorough the trade of infected plants.

Following completion of the study, the researchers looked through historical catalogues of large commercial nurseries in Italy and France and found records of mature Monterey cypress trees for sale during the late 1920s and 1930s, indicating significant imports of the California trees and their seeds at that time.

“It is very likely that the pathogen was introduced during that period,” said Danti, who added that interviews the research team conducted with people who worked in the nurseries then suggested that cypress canker disease was becoming a problem by the late 1930s.

The researchers found three progenitor strains of the pathogen only in Tuscany, indicating that the disease was brewing there for several generations before exploding beyond the region’s borders.

“It could have easily taken 10 to 20 years from the time of introduction for the first major outbreak to occur,” said Garbelotto. “In Italy, the pathogen was first identified in 1951, so it could have arrived decades earlier.”

The study authors advocate the genetic screening of plants to stem the spread of the disease, just as plant shipments in and out of California are now tested for the Sudden Oak Death pathogen.

“We can develop tests to screen for the presence of S. cardinale on plants that are traded, and even to test for the presence of strains that are currently not present in Europe or in the Southern Hemisphere,” said Garbelotto. “Technological advancements of the last few years allow for the easy development of such tests, but it was essential to figure out the source of the pathogen in order to know what to look for.”

Garbelotto said that researchers in Europe have spent the past three decades developing cypress trees that are resistant to the current variant of S. cardinale in the region.

“There is no assurance those resistant trees will be resistant to other strains from California, if they are introduced,” said Garbelotto. “If another strain were to be introduced into the Mediterranean or in the Southern Hemisphere, this could accelerate and worsen the epidemic in those regions. It could nullify a 30-year long effort to develop trees that are resistant to the pathogen.

“It is imperative to stop the movement of infected plants in order to avoid further introductions that could completely overcome those lines of resistant trees.”

Be careful what you plant

The new study spotlights the hazards of planting trees and other vegetation in regions where they are not native. Garbelotto said consumers should be careful about what they choose to plant in their backyards.

“Gardeners tend to pick the easiest plant to grow,” said Garbelotto. “Monterey cypress became very popular in Europe because they grow faster, and they grow really well along the shore, while the Italian cypress is better suited for inland regions. The popularity of the Monterey cypress may have inadvertently led to the devastating spread of a deadly fungus throughout the world.”

Garbelotto added that the cypress canker pathogen is so aggressive that, even in California, it can kill trees that are planted outside of their natural range.

“When Monterey cypress trees are planted in Monterey or along the coast, they are resistant to the disease,” said Garbelotto. “That suggests that in coastal areas, the environment is unfavorable for development of infections, despite the pathogen having been in California for a long time. The pathogen emerges when we place the tree in a foreign environment.”

Garbelotto said that chemical treatments for cypress canker disease may become available in the near future, but they are costly, and their effects on the environment are not clear, so prevention is preferable.

To confirm the connection between California and Mediterranean populations of the pathogen, the researchers have conducted a follow-up study using more than 200 genetic markers of S. cardinale isolates. Results of the study should be available within the next year.

Sarah Yang | EurekAlert!
Further information:

More articles from Agricultural and Forestry Science:

nachricht “How trees coexist” – new findings from biodiversity research published in Nature Communications
21.03.2018 | Technische Universität Dresden

nachricht Earlier flowering of modern winter wheat cultivars
20.03.2018 | Georg-August-Universität Göttingen

All articles from Agricultural and Forestry Science >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Researchers at Fraunhofer monitor re-entry of Chinese space station Tiangong-1

In just a few weeks from now, the Chinese space station Tiangong-1 will re-enter the Earth's atmosphere where it will to a large extent burn up. It is possible that some debris will reach the Earth's surface. Tiangong-1 is orbiting the Earth uncontrolled at a speed of approx. 29,000 km/h.Currently the prognosis relating to the time of impact currently lies within a window of several days. The scientists at Fraunhofer FHR have already been monitoring Tiangong-1 for a number of weeks with their TIRA system, one of the most powerful space observation radars in the world, with a view to supporting the German Space Situational Awareness Center and the ESA with their re-entry forecasts.

Following the loss of radio contact with Tiangong-1 in 2016 and due to the low orbital height, it is now inevitable that the Chinese space station will...

Im Focus: Alliance „OLED Licht Forum“ – Key partner for OLED lighting solutions

Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology FEP, provider of research and development services for OLED lighting solutions, announces the founding of the “OLED Licht Forum” and presents latest OLED design and lighting solutions during light+building, from March 18th – 23rd, 2018 in Frankfurt a.M./Germany, at booth no. F91 in Hall 4.0.

They are united in their passion for OLED (organic light emitting diodes) lighting with all of its unique facets and application possibilities. Thus experts in...

Im Focus: Mars' oceans formed early, possibly aided by massive volcanic eruptions

Oceans formed before Tharsis and evolved together, shaping climate history of Mars

A new scenario seeking to explain how Mars' putative oceans came and went over the last 4 billion years implies that the oceans formed several hundred million...

Im Focus: Tiny implants for cells are functional in vivo

For the first time, an interdisciplinary team from the University of Basel has succeeded in integrating artificial organelles into the cells of live zebrafish embryos. This innovative approach using artificial organelles as cellular implants offers new potential in treating a range of diseases, as the authors report in an article published in Nature Communications.

In the cells of higher organisms, organelles such as the nucleus or mitochondria perform a range of complex functions necessary for life. In the networks of...

Im Focus: Locomotion control with photopigments

Researchers from Göttingen University discover additional function of opsins

Animal photoreceptors capture light with photopigments. Researchers from the University of Göttingen have now discovered that these photopigments fulfill an...

All Focus news of the innovation-report >>>



Industry & Economy
Event News

Virtual reality conference comes to Reutlingen

19.03.2018 | Event News

Ultrafast Wireless and Chip Design at the DATE Conference in Dresden

16.03.2018 | Event News

International Tinnitus Conference of the Tinnitus Research Initiative in Regensburg

13.03.2018 | Event News

Latest News

TRAPPIST-1 planets provide clues to the nature of habitable worlds

21.03.2018 | Physics and Astronomy

The search for dark matter widens

21.03.2018 | Materials Sciences

Natural enemies reduce pesticide use

21.03.2018 | Life Sciences

Science & Research
Overview of more VideoLinks >>>