The Australian host of a weekend family lunch is on trial charged with murdering her estranged husband's parents and an aunt and attempting to murder an uncle with poisonous mushrooms. Prosecutor Nanette Rogers opened her case on Wednesday against Erin Patterson, 50, in the Victoria state Supreme Court. Patterson has pleaded not guilty to all charges.

She served meals of beef Wellington, mashed potato and green beans at her home in the rural town of Leongartha on July 29, 2023. Her guests included her parents-in-law Gail and Don Patterson, both 70, Gail Patterson's sister Heather Wilkinson, 66, and Wilkinson's husband, Ian Wilkinson, 68.

All four guests were hospitalised the next day with poisoning from death cap mushrooms, also known as amanita phalloides, that were added to the beef and pastry dish. Ian Wilkinson survived after a liver transplant.

Erin Patterson's husband, Simon Patterson, 50, was also invited to the lunch but declined.

The jury was told on Tuesday that prosecutors had dropped three charges that Erin Patterson had attempted to murder her husband, whom she had been separated from since 2015.

The court heard that Patterson had previously dehydrated mushrooms and added them to her daughter's muffins without telling her. She claimed she did this because her daughter had said she didn't like mushrooms.

The jury was also told she had covertly mixed dehydrated mushrooms into chocolate brownies made for her children.

Two weeks before the poisoning, Erin Patterson had invited her husband and his relatives to lunch while she was attending a Korumburra Baptist Church service where Ian Wilkinson was the pastor. Simon Patterson initially accepted the invitation.

"She said the purpose of the lunch was to discuss some medical issues that she had and to get advice about how to break it to the kids," Rogers said.

"The accused said that it was important that the children were not present for the lunch," Rogers added.

The Wilkinsons were surprised by the invitation because they'd never been to Erin Patterson's large five-bedroom house.

When Heather Wilkinson was taken to the hospital the next morning, she told Simon Patterson she had been puzzled by Erin Patterson eating from a different plate than those served to the guests.

"I noticed that Erin put her food on a different plate to us. Her plate had colors on it. I wondered why that was. I've puzzled about it since lunch," said Heather Wilkinson, according to the prosecution.

Simon Patterson told his aunt that his wife might have run out of plates.

Rogers told the jury that Erin Patterson fabricated an ovarian cancer diagnosis to explain why her children didn't attend the lunch.

"After the lunch, the accused announced that she had cancer and asked for advice on whether to tell the children or to keep it from them," Rogers said.

"They had a discussion about it being best to be honest with the children. They prayed as a group for the accused's health and wisdom in relation to telling the children," Rogers added.

Defense lawyer Colin Mandy told the jury his client never had cancer and that the guests had been poisoned by mushrooms she had served, but that the poisoning was accidental.

"The defense case is what happened was a tragedy. A terrible accident," Mandy said.

Rogers told the jurors that she she would not provide a motive for the poisonings.

"You might be wondering now why would the accused do this? What is the motive? You might still be wondering this at the end of this trial," Rogers said. "You do not have to be satisfied what the motive was or even that there was a motive."

Two days after the lunch, Erin Patterson went to the hospital complaining of diarrhea and nausea. By then, medical staff had diagnosed her guests as suffering death cap poisoning.

Erin Patterson told authorities that she had cooked with a mixture of fresh mushrooms bought from a supermarket and dried mushrooms bought from an Asian food store.

Mandy said his client had lied to police when she said she hadn't foraged for wild mushrooms.

"She did forage for mushrooms. Just so that we make that clear, she denies that she ever deliberately sought out death cap mushrooms," Mandy said.

Doctors insisted that Erin Patterson's two children, then aged 9 and 14, be tested because their mother said they had eaten beef Wellington leftovers.

Erin Patterson said the children were safe because she had scraped the pastry and mushrooms from the steak. She explained the children didn't like mushrooms.

Rogers said Erin Patterson had not eaten poisonous mushrooms and had not fed her children the lunch leftovers. Mandy said she had eaten the mushrooms but had become less sick than the others.

The trial was adjourned until Thursday and is expected to continue for six weeks. She is charged with three counts of murder and one of attempted murder. Murder carries a maximum penalty of life imprisonment and attempted murder carries a maximum 25 years in prison.