In 2010, the bacterial disease Psa-V was detected in a Bay of Plenty orchard, leading to losses for many North Island kiwifruit growers. The gold kiwifruit variety Hort-16A proved susceptible to the disease, which later spread to other North Island regions, including Northland, the Coromandel, and the Waikato. The disease did not spread to the South Island.
A system was developed by kiwifruit breeders and scientists to prevent the movement of the disease. "The way we are doing it in New Zealand is more stringent than what we're doing if we're exporting material," said Dr Ed Morgan of the Bioeconomy Science Institute.
Following the outbreak, the institute worked with Zespri to establish a pathway for moving plant material from the North Island to the South Island without transferring the disease. This enables South Island growers to access cultivars and supports breeding work at the Kiwifruit Breeding Centre in Motueka.
Plant material is developed from budwood and transferred to a laboratory in Palmerston North after four to five weeks. Tissue cultures are then established and subjected to multiple disease checks, including a PCR test by an external lab to detect Psa-V. Only plants that pass all checks are approved for transfer.
Once in the South Island, plantlets measuring 2 to 5 centimetres are held at the Bioeconomy Science Institute in Lincoln. They remain in a glasshouse for six months with weekly monitoring for symptoms. After this stage, plants undergo another PCR test, followed by eight months in pots through a spring and summer growing cycle, again with monitoring and a final PCR test.
Plants that pass these stages are then held for a further year either at the Lincoln site or in a nursery outside South Island growing regions.
Kiwivine Health oversees this pathway under a regulatory plan aligned with the Biosecurity Act. The organisation audits the process annually and manages disease prevention across the industry.
While newer kiwifruit varieties are less susceptible, Psa-V remains present. "There needs to be active prevention programs in place every season, to make sure that it doesn't become an issue and infections don't run rampant on orchards," said KVH chief executive Leanne Stewart.
The pathway currently handles about 120 plants per year, with no detection of Psa-V in plants transferred to Lincoln. Stewart noted that South Island varieties such as Heyward, Sun Gold, and Ruby Red remain susceptible, requiring continued management.
Source: RNZ
