Report: Pollen can carry disease

Fifty-one New Zealand kiwifruit orchards have now tested positive for the bacterial disease Psa. Photo / Christine Cornege

Officials say kiwifruit pollen imports were not routinely tested for the bacterial disease Psa because science said it could not be a carrier - but an Italian industry bulletin in May stated that it could.

The source of the outbreak threatening the industry has yet to be determined, but growers have speculated that the import of infected pollen is a possible cause.

Fifty-one orchards have been confirmed with the bacterial disease, which had a devastating impact in the Italian region of Lazio.

Ministry of Agriculture and Forestry biosecurity response manager David Yard this week said import health standards were based on the best available scientific knowledge and there was no scientific literature to suggest Psa could be transmitted in pollen.

"So we haven't incorporated a routine test for Psa in pollen before entry," he said.

"Certainly if pollen is proved to be a vector [carrier] of Psa, it's a new discovery as far as we are aware anyway."

However, a bulletin for the Italian industry in May said work by Plant & Food Research in New Zealand had found Psa present on pollen collected from a badly infected vine in Italy.

"This suggests that pollen could be a possible vector of the disease," the bulletin said.

MAF said the research had not been formalised, peer reviewed or published in a scientific sense.

The first correspondence MAF received about suspected Psa contamination of pollen from Plant & Food was an email on September 30 to alert them to preliminary findings.

In an email from exporter Zespri on October 5, pollen was mentioned as able to carry live cells of Psa and a recommendation was made that pollen from infected orchards should not be imported, MAF said.

Imports of pollen required collection from closed flowers to avoid contamination, MAF said.

The last import of pollen for pollination was on June 16, after which date there were two small laboratory samples in August and September.

Only kiwifruit pollen from Chile, which was free from Psa, had been applied to vines.

Permits for importing pollen were cancelled in November as a precaution, at which time the response to Psa was under way.

Imported pollen stock had been impounded.

"MAF stands by its [import health standard] which remains based on the fact there is still no internationally published research establishing pollen as a pathway for entry and establishment of Psa," MAF said.

"MAF cannot base its trade and importation requirements on a paragraph in a trade newsletter."

It said international obligations when setting import requirements were that specific measures were imposed only where technically justified, "that is having robust scientific information to support them".

"To put in place what is effectively a trade barrier on the basis of some unfinished research would not be appropriate," MAF said.

"Note that under international trading rules emergency precautionary measures may be imposed provided research is conducted that will justify (or otherwise) those measures, and this was the action taken to withdraw the permits in November."

Yard said some infected orchards had used imported pollen, although some growers had reported symptoms of Psa before it was used.

"Which rather does question whether it is in the imported pollen."

Plant & Food spokesman Roger Bourne said the research was at an early stage and had not been peer reviewed or published.

The pollen from Italy was a couple grams and imported under appropriate protocols for research, he said.

"The research, which has only been going on in Italy for a couple of years since it really manifested itself as a huge problem there, hasn't got to a stage where it can help New Zealand immediately now," Bourne said.

Normally Plant & Food would alert MAF if it thought the issue was significant, but the science would have to have been peer reviewed and publishable.

"Otherwise we could go to MAF every day with a supposition on things."

MAF said initial tests on imported and local pollen samples had indicated some level of Psa but were deemed inconclusive because of possible cross-contamination.

Gauging the impact
* Pseudomonas syringae pv actinidiae (Psa) is a bacterial vine disease which affects kiwifruit species.
* 51 orchards have tested positive for the disease.
* Can be spread by airborne spores or on equipment.
* Does not affect plants other than the vine.
* No risks to human health.