Growing Futures

Speeding up disease diagnosis

Speeding up disease diagnosis

New tools to diagnose Psa allows growers to make orchard management decisions faster

New Zealand is the third largest producer of kiwifruit in the world, earning close to $1 billion in exports each year. In November 2010, the kiwifruit disease Pseudomonas syringae pv actinidiae (Psa) was discovered in New Zealand, making tools to manage the disease vital for the continued success of the industry.

Two strains of the Psa bacterium have been identified in New Zealand orchards. The virulent strain, known as Psa-V, causes major damage to the plant eventuating in plant death, whereas the less virulent strain, Psa-LV, causes only benign symptoms which do not significantly affect the fruit quality or yield. The presence of Psa-V on an orchard requires more rigorous and on-going management – in the case of Hort16A, the complete removal of infected vines was the most effective way of controlling spread of the disease. However, each initially presents as leaf spotting, and there is no visible way to distinguish between the two strains at an early stage.

Speeding up diagnosis

In 2011, a new test was developed to identify which strain of the Psa bacterium is present in an orchard. The new test typically returns a result in two to three days, allowing growers and industry groups to quickly make decisions on how best to manage the orchard to limit spread of the disease.

Prior to the introduction of the DNA-based test, growers could wait up to two weeks for a diagnosis of the Psa disease, with no information on the strain present. During this time any vines infected with the bacterium could develop severe symptoms and the bacterium could spread to infect other vines or orchards nearby. The introduction of the test allows growers to quickly determine whether vines are infected with Psa-V and what management steps to take.

The Psa research programme is funded by Zespri Group Limited, KVH, the Ministry of Business, Innovation & Employment and Plant & Food Research.

Created: September 2014

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