Growing Futures

Breeding for Psa resistance

Breeding for Psa resistance

The bacterial disease Psa was identified in New Zealand in November 2010. Resistance to the disease is now a key characteristic for the kiwifruit breeding programme

Kiwifruit is a New Zealand icon, and the nation is the third largest producer of the fruit in the world. The New Zealand kiwifruit industry exports around $1 billion of produce every year, primarily to European and Asian markets. The New Zealand-bred ‘Hort16A’ cultivar, marketed globally as ZESPRI®GOLD Kiwifruit, demands a premium in the marketplace because of its novel gold-coloured flesh and sweet tropical flavours.

In 2010, the bacterial disease Psa (Pseudomonas syringae pv. actinidiae) was discovered in New Zealand, making strategies and tools for managing the disease key to the continued success of the industry. By the end of June 2012, more than 35% of New Zealand kiwifruit orchards were infected with the virulent form of the bacterium, Psa-V. 

Finding a replacement cultivar

‘Hort16A’ is particularly susceptible to Psa and identification of a new cultivar to replace ZESPRI®GOLD Kiwifruit in key premium markets was vital to the long-term sustainability of the industry. The Plant & Food Research kiwifruit breeding programme had previously delivered three new cultivars for pre-commercial trials. One of these, known as Gold3 and marketed as ZESPRI®SUNGOLD Kiwifruit, was chosen originally to widen the market window for New Zealand kiwifruit, as it was predicted to enter markets up to three weeks ahead of the existing ‘Hort16A’ cultivar. The introduction of Psa resistance screening on the research orchard identified Gold3 as tolerant to the disease. Subsequently, the commercialisation of the cultivar was fast-tracked, and, in 2012, more than 2,000 hectares of Gold3 plants were released to growers. More than 75% of these will be allocated to replace ‘Hort16A’ plantings that have been destroyed by the disease.

Maintaining industry sustainability

The release of Gold3 is the first step in the recovery pathway of the industry. A combination of refined orchard management techniques and new cultivars with improved resistance to the disease are expected to allow the kiwifruit industry largely to recover its current market position by 2016. As a consequence, marketer ZESPRI Group Limited has revised its growth trajectory, delaying its target of $3 billion per annum by four years to 2029.

The Plant & Food Research kiwifruit breeding programme has expanded its capacity, and has increased the number of new seedlings being screened from 20,000 to 50,000 and, over time, potentially to as many as 400,000 per annum. Whilst Psa resistance is a key characteristic in the breeding programme, other commercial traits such as agronomic performance, flavour and health are still essential to the success of a future cultivar. New technologies are also being developed to speed up the rate at which cultivars with tolerance to Psa can be identified. This includes research into the molecular basis of Psa resistance to support the development of genomics tools to identify plants in the breeding programme with intrinsic resistance to the disease.

The kiwifruit breeding programme is funded by the Ministry of Business, Industry and Employment with additional investment by ZESPRI Group Limited and Plant & Food Research.

Created: September 2012

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