New species of bacteria killing palm trees in Australia

While investigating a disease outbreak at a botanical garden in Queensland, scientists have discovered a new species of bacteria that causes a deadly disease in palm trees.

The bacterium, called Candidatus Phytoplasma dypsidis, was found to cause the deadly wilting disease. This new discovery was reported in the International Journal of Systematic and Evolutionary Microbiology.

In 2016, several ornamental palms in a greenhouse at a botanical garden in Cairns, Queensland, mysteriously died. A sample was taken from one of the diseased plants and examined by Dr. Richard Davis and his colleagues from the Australian government’s Department of Agriculture, Water and Environment, as well as state and local government officials.

They compared the characteristics and genome of the bacterium identified as the cause of the disease and found that the bacterium was similar to other Candidatus Phytoplasma species, many of which are responsible for palm disease epidemics elsewhere, but different enough from them to be an independent species. “When laboratory tests showed that it was something close but not the same as the destructive palm pathogens overseas, we were very surprised,” Dr. Davis said.

“At first we thought it was probably an unrelated fungal disease. Almost in the end I suggested we test for phytoplasma because very dangerous phytoplasma diseases of palm trees are common all over the world, including neighboring Papua New Guinea,” he explained.

To date, Candidatus Phytoplasma dypsidis infection has been found to cause disease in 12 different palm species, including Cocos nucifera, which grows coconuts. “Although palms are not grown as a cash crop in Australia, they are important ornamental garden and cultural plants. Coconuts and other palms are an economically significant component of Australia’s tropical tourism industry,” says Dr. Davis.

Palm trees are becoming much more important in most countries near Australia in Southeast Asia and the Pacific, where coconuts are the “tree of life.” It is important to raise awareness of an emerging disease threat such as this so that regional biosecurity measures are a priority.”

The assumption is that the bacterium spreads from plant to plant by insects that feed on the phloem, the tissue that carries nutrients through the plant, Dr. Davis said, “From our observations of how this thing has spread through the local area, it follows that the vector must be insects. Figuring out what species of vectors are involved is a vital next research priority.”

A number of questions remain, including which insect vectors spread the disease and whether the bacterium can infect other plant species, including important crops such as bananas.

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