California is being invaded by the world’s deadliest mushroom

Mechanisms driving the spread of the fungus have remained unclear

Vishwam Sankaran
Thursday 16 February 2023 11:00 GMT

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Scientists have found that the world’s deadliest mushroom has been rapidly invading California, likely by cloning itself – an advance that sheds light on the reproductive strategies used by the fungus under different conditions.

The “death cap” mushroom, scientifically known as Amanita phalloides, has been known to kill a handful of people each year, and sicken many more humans as well as animals in the US.

These mushrooms, when mature, have a broad, off-white cap, measuring several inches tall and across and have a rounded cap when they are immature, scientists say.

Toxins within the mushroom can damage the body’s cells, particularly to liver and kidney tissue, and can become deadly when its exposure leads to liver failure.

Eating even a single mushroom can be fatal to an adult human, and some estimates suggest it may account for nearly 90 per cent of global deaths from mushrooms worldwide.

However, the mechanisms driving the spread of the fungus are not understood, say researchers, including those from the University of Wisconsin-Madison in the US.

Traditionally mushrooms are known to reproduce in the wild bisexually, which involves the underground structures of two individuals fusing and producing mushrooms above the ground that contain genetic material from both parents.

In the new study that is yet to be peer reviewed, posted in the pre-print server bioRxiv, scientists found that the Californian version of the death cap mushroom fertilises itself, instead of waiting for a mate – a process that is rarely observed in mushrooms outside of labs.

The Californian death cap mushrooms have been across the US west coast and are becoming more abundant than they were in the native European lands of A. phalloides.

“The diverse reproductive strategies of invasive death caps are likely facilitating its rapid spread, revealing a profound similarity between plant, animal and fungal invasions,” scientists wrote in the study.

While it remains unclear how the Californian death caps have achieved self-fertilisation, scientists suspect it may be bypassing genetic prosses that traditionally ensure that these mushrooms are only made after two individuals fuse.

“The fungus is both unisexual and bisexual, revealing a previously unsuspected reproductive flexibility in a natural population of death caps,” scientists explained in the study.

“The spread of A. phalloides in California is likely facilitated by its ability to sporulate without mating with another individual,” they added.

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