A group of kiwifruit growers claiming that negligence by the Ministry for Primary Industries allowed the Psa virus into New Zealand in 2009 isn't legally able to make a damages claim and is wrong about where the virus began, a government lawyer has told the High Court.

The case, which began in Wellington's High Court last month, involves a group of 212 growers, led by Strathboss Kiwifruit and Seeka.

They claim the Ministry of Agriculture and Forestry (MAF) - which became part of MPI when that ministry was formed in 2012 - was negligent under the Biosecurity Act, which made it responsible for controlling the importation of "risk goods".

The bacteria infected 80 per cent of kiwifruit orchards nationwide and is estimated to have cost the industry up to $930 million in lost exports.

When Seeka joined the class action in 2014, it estimated the Psa bacteria had cost it more than $45 million and prompted it to slash its workforce by 40 percent to mitigate the impact of the outbreak.

The country's kiwifruit marketing body, Zespri International, has not joined the action and has urged others against it.

The government's lawyer, Jack Hodder QC, presented the Crown's opening arguments today. He said that the statutory responsibility held by the ministry for managing biosecurity risks "does not give rise to private law claims for damages such as those advanced by the plaintiffs", and the claims made are "misconceived in law and unsupported on the evidence."

Hodder said the group's arguments, if successful, would mean the government would be held financially liable if a biosecurity failure due to its error or insufficient effort resulted in industry losses.

"But the duty would have even wider implications than that," the opening submissions say.

"Because New Zealand's decided cases have not recognised a common law duty of care owed by public servants when exercising functions in the general public interest, a finding in favour of the plaintiffs on duty would have ramifications across the whole government, not just those functions exercised in respect of the border."

In his opening submissions in August, the kiwifruit grower group's lawyer, Davey Salmon, said MAF had known for many years that Psa was a significant pest and would cause economic harm to kiwifruit.

"They should not have allowed imports of kiwifruit pollen without carrying out an analysis of the risks, including the risk of introducing Psa," Salmon said.

"The conditions imposed for pollen imports were wholly inadequate. On any view, there was a failure to exercise reasonable care."

The grower group says in 2009, Kiwi Pollen imported two shipments from China; the first of 4.5 kilograms of kiwifruit anthers, the pollen-bearing part of a male flower's stamen, from an orchard outside Xi'an in Shaanxi Province, China.

It says DNA evidence shows the strain of Psa found in New Zealand is nearly identical to a strain isolated in Shaanxi in 2010, and an element of the main chromosome in the New Zealand strain has only been found in one other strain in the world - the Shaanxi strain.

The government's submissions say that MAF officers "behaved reasonably" and weren't negligent and that the pollen imported was not the source of the Psa outbreak.

The timing of the Psa symptoms being noticed meant that the pollen imported was not likely to be the source of infection, there was no evidence the pollen had been applied to any orchards, and the chance of accidental cross-contamination is "so unlikely as to be purely speculative," it says.

Even if those arguments are disregarded, the crown says it is immune from liability under the Biosecurity Act, as the plaintiffs can't show officials acted without reasonable cause.

The case is set down for about three months.

-NEWSIE.