Three attempted murder charges relating to Erin Patterson's estranged husband have been discontinued by prosecutors, jurors have been told.
Patterson, 50, is facing the first day of a Supreme Court jury trial in the small town of Morwell, about two hours' drive from Melbourne.
The trial has attracted significant national and international media interest, with dozens of journalists, documentary-makers, true crime writers and podcasters flooding the small town.
She has pleaded not guilty to three murder charges and one of attempted murder over an allegedly poisonous mushroom meal at her Leongatha home in July 2023.
Patterson is accused of killing her former in-laws, Don and Gail Patterson, and Gail's sister Heather Wilkinson.
Ms Wilkinson's husband Ian, for whom Patterson is charged with attempted murder, also became ill after the lunch but survived the ordeal.
A jury of 15 from Victoria's Gippsland region were selected on Tuesday, made up of 10 men and five women.
Patterson sat in the court dock wearing a pink and white striped shirt and silently watched Justice Christopher Beale as he instructed the jury on Tuesday afternoon.
"You represent one of the most important institutions in our community, the institution of trial by jury," he said.
"And so it is for you, the jury, and you alone to decide whether she is guilty or not guilty of the crimes alleged against her.
"You alone are the judges of the facts."
He then informed jurors that three attempted murder charges, involving Patterson's former husband Simon, had been discontinued by the prosecution.
"The accused was charged by police with three counts of attempted murder in relation to her estranged husband Simon Patterson," Justice Beale said.
"Those charges have been discontinued by the Director of Public Prosecutions.
"In other words, those charges have been dropped and you must put them out of your mind."
Justice Beale also urged the jury not to read the news, watch television or engage in social media content about the trial.
"Dont risk your opinion as judges of the facts being contaminated, you must base your decision only on the evidence presented to you here in court," he said.
The prosecution, led by Nanette Rogers SC, will deliver their opening address to the jury on Wednesday morning.
Patterson's barrister Colin Mandy SC will then deliver the defence's reply, before the first witness is expected to be called on Thursday.
Due to the high level of interest, only six seats inside the court room will be allocated to media each day of the trial with the rest given to members of the public.
The jury of 15 will be whittled down to 12 to decide unanimously whether Patterson is guilty or not guilty of the three murders and one attempted murder.
Justice Beale said the 12 jurors would be sequestered when they retire for deliberations.
The trial is expected to run for five to six weeks.