Biosecurity officials say samples of kiwifruit pollen collected from the Bay of Plenty and South Auckland over the past two years contain the bacteria that cause vine canker.

DNA testing showed the Pseudomonas syringae pv actinidiae (PSA) bacteria in pollen collected in 2009 and 2010, though the Ministry of Agriculture and Forestry noted there was no firm evidence that this contamination can infect plants.

Growers have been increasingly concerned that some of the 300 tonnes of male flowers picked each year for their pollen to be used in fertilising crops may have been taken from infected vines.

Though about 80,000 beehives are brought into orchards during flowering to pollinate vines, growers have made increasing use of artificial pollination in recent years, with an estimated 20 per cent to 30 per cent of the nation's kiwifruit orchards supplementing the job done by bees.

About three tonnes of pollen collected in New Zealand is sprayed or blown on to the vines, to aid pollination because the vines do not naturally attract bees.

During the past two years, 77kg of pollen has been imported from Chile and 2kg from China. The Chilean pollen was applied to crops, while that from China was for laboratory testing.

Initial DNA testing last weekend of kiwifruit pollen imported from Chile showed a single positive result for the vine canker bacteria.

Biosecurity officials suspended imports and froze remaining stocks of imported pollen during the week, though retesting of the Chilean pollen did not produce any positive results.

"There is no current evidence to show that PSA in pollen can infect healthy kiwifruit vines," said MAF response manager, David Yard.

"There is no firm evidence that artificial pollination is causing PSA disease."

Because many infected orchards had not used artificial pollination, "other mechanisms of spread may be more significant".

Further testing of historical samples will be carried out but the results in domestic pollen pre-dating the imports suggested imported pollen may not be the original source of infection.

On November 14, MAF warned growers that pollen might be a carrier for the bacteria and suggested that if they had to use artificial pollination, pollen collected from their own property might present a lower risk.

"Growers may wish to ensure that pollen used on their orchards is tested for Psa before they pollinate," MAF said today.

Imports of kiwifruit pollen were not routinely tested at the border for the disease, and MAF this week said this its import health standard for pollen had been based around the best available scientific knowledge at the time.

There was no peer-reviewed scientific evidence that pollen was a pathway for the transmission of bacteria, and the pollen was collected as closed flowers "and thus is protected from possible contamination", MAF said before today's announcement.

Biosecurity Minister David Carter this week fended off a call for an immediate ban on pollen imports after Federated Farmers said there was a strong possibility the Psa kiwifruit vine disease got into New Zealand in imports.

The federation's biosecurity spokesman, John Hartnell, said the imported pollen was not being adequately checked for plant or bee diseases it may be carrying but Mr Carter told Federated Farmers those sorts of claims were premature.

- NZPA