MAF Biosecurity New Zealand says tests show the kiwifruit vine-killing bacteria Psa has been in the country since as far back as 2007 and that imported pollen is not to blame for the crisis.
MAF's Psa response manager David Yard says New Zealand pollen collected from the Bay of Plenty and South Auckland last year has tested positive for the disease, while samples taken in 2007 have also returned weak positive results.
Mr Yard says these samples were taken before imported pollen was used on orchards in New Zealand.
He says because there are historical examples that predate any artificial pollination using imported pollen, it suggests that imported pollen is not the root of entry of the bacteria into the country.
Mr Yard says only about half of the 51 infected orchards have used artificial pollination.
He says people, wind or an as-yet identified cause could be behind the spread.
The number of orchards confirmed to have the bacterial disease stands at 51, up from 37 on Thursday.
Psa strategy agreed
Kiwifruit representatives from across the industry have voted in favour of an aggressive approach to the vine-killing disease Psa.
At the meeting, in Tauranga on Friday evening, the Kiwifruit Industry Advisory Council authorised $25 million of industry funding to match the $25 million being contributed by Government.
The meeting followed a series across the country on Thursday and Friday attended by more than 1500 growers.
Zespri says its $25 million will come from existing reserves within the GOLD payment pool initially, and will be supplemented by contributions from grower pools and a reduced grower rebate from 2011.
Growers also agreed to the establishment of a new entity to coordinate a long-term management programme and further research and development into understanding and mitigating the impact of Psuedomonas syringae pv actinidiae, or Psa.