Opportunities for environmental modification to controlPseudomonas syringaepv.actinidiaein kiwifruit

Abstract

Bacterial canker of kiwifruit (Pseudomonas syringae pv. actinidiae; Psa) was first identified in New Zealand kiwifruit orchards in 2010. The bacterial disease has impacted significantly on orchard productivity. 'Hort16A' (Actinidia chinensis), one of the main cultivars in production in 2010, proved susceptible to the disease with large areas now removed. A new Actinidia chinensis cultivar ('Gold3'), with improved tolerance to Psa, has now been released. The kiwifruit industry has made considerable advances in understanding Psa, and extensive research efforts have focussed on control options, including cultivar selection, agrichemical treatments and changes in vine management practices. It is recognised that continued productivity of kiwifruit orchards will involve the adoption of a suite of Psa disease-mitigating practices. Modification of environmental conditions is being explored through the construction of large plastic canopies over orchards. Moisture is required for Psa multiplication and vine infection; the plastic canopies minimise leaf moisture and prevent rainfall from spreading bacteria within the canopy. Additional benefits include protection from wind and frost, environmental conditions that can result in physical damage to the vines, predisposing them to infection. Within a year of the first canopies being constructed, approximately 30 ha of the 'Gold3' has been covered. Research trials have indicated that the canopies reduce the progression of Psa symptoms when covers are constructed over vines with low levels of infection. As the area of kiwifruit production under plastic canopies continues to increase, effects on minimising the impacts of Psa continue to be monitored, and impacts on vine physiology, fruit production and occurrence of other pests and diseases are being explored.