Researchers at UC Berkeley have found that the spread of a cypress tree-killing pathogen to six continents very likely originated in trees exported from California to Europe in the 1920s.
The study, published Thursday in the journal Phytopathology, determined that the cypress canker disease — Seiridium cardinale — has infected approximately 95 percent of native trees in the cypress family. The study was a collaboration between the Italian National Research Council and Matteo Garbelotto, campus adjunct associate professor of environmental science.
The pathogen, which was first discovered in California in 1928, later spread to New Zealand and France and was soon reported to have spread throughout southern Europe, according to Garbelotto. The fungus, which chokes off the tree’s water supply, enters through cracks in the bark on the branches.
“The end result is that if the pathogen is aggressive, it can take out an entire tree species,” Garbelotto said.
According to Garbelotto, the fungus is very versatile, allowing it to spread from tree to tree. It could affect the trees in a way similar to Sudden Oak Death, which resulted in the death of thousands of California oak trees after a pathogen jumped from a rhododendron to an oak.
“The connections (among plant species) are infinite, so losing trees is not a small problem,” said Garbelotto.
Garbelotto said a large part of the problem was — and is — the introduction of non-native tree species to the tree industry, which imports and exports trees all over the world.
Travis Woodard, general manager of Urban Tree Farm Nursery in Fulton, Calif., said cypress trees are the only trees that the company does not purchase out-of-state, a measure that can reduce infestations.
“Pests are a part of the business,” Woodard said. “It doesn’t mean it’s the end of the world. It’s part of agriculture.”
The researchers will continue their study of the pathogen, particularly in understanding how the fungus evolves once it takes hold of a tree.
Gregory Gilbert, a professor of environmental studies at UC Santa Cruz, previously worked with Garbelotto at UC Berkeley to study the biogeography of wood decay fungi in tropical mangrove forests and the diversity of fungi living in the leaves of tropical trees.
“Plants and their pathogens are in a constant co-evolutionary dance, where pathogens evolve a bit of an advantage over their hosts so they can cause more disease and reproduce more,” Gilbert said in an email. “Knowing the origin of an introduced pathogen, how many times it has been introduced, whether it is reproducing sexually, and how much genetic diversity is found in the pathogen are all keys to making best guesses about likely future dynamics of a novel epidemic and to developing effective means of control.”