Pseudomonas syringae pv. actinidiae (Psa) is a bacteria that can result in the death of kiwifruit vines. It was first discovered in New Zealand in November 2010 and rapidly caused widespread and severe impacts to NZ's kiwifruit industry.
Photo: Psa magnified 6000 times
Pseudomonas syringae pv. actinidiae (Psa) carries no risks associated with human or animal health and does not affect plants other than kiwifruit vines. Psa is believed to be spread by weather events, namely wind and rain, and plant material. It is also believed to be spread by footwear, vehicles and orchard tools. In an orchard it can exist as:
Growth of the bacteria outside/inside the vines can result in leaf spotting, cane/leader dieback and, in extreme cases, vine death accompanied by the production of exudates. Click here for a Psa-V Symptoms Guide.
Since it's discovery in 2010 a significant amount of funding and resource has gone into a Psa-V research & development programme and product testing programme to better understand and manage the disease.
Based on the results of these programmes, and on-orchard experience, KVH has developed a Psa-V Best Practice Guide to assist growers with managing the disease.
Non-New Zealand strains of Psa
Different outbreaks of Psa have been caused by five related, but genetically distinct lineages of Pseudomonas syringae and it is likely that many more exist in wild kiwifruit populations.
Psa1 (Japan, Italy) and Psa2 (Korea), are of particular concern as these strains are more virulent against Hayward cultivars than the Psa-V strain currently in NZ.
New genetic material of any strain is a concern due to the potential of horizontal gene transfer and the impact new strains may have on new or existing kiwifruit cultivars.
New strains of Psa are also expected to evolve within New Zealand of which the characteristics and virulence to new and existing kiwifruit cultivars are unknown. Good biosecurity practices are vital to prevent the spread of any new strains between orchards and growing regions.