Recent progress on control of Pseudomonas syringae pv. actinidiae

Following the discovery of Pseudomonas syringae pv. actinidiae (Psa ) in New Zealand, a massive screening programme on young kiwifruit plants in a glasshouse was conducted in the hope of finding new compounds for the control of this pathogen. Unfortunately, control of plant pathogenic bacteria is difficult, and Psa is no exception. Some of the difficulties with controlling Psa come from its ability to survive and to colonise tissues without causing symptoms, and its ability to resist inhibitory compounds by forming a biofilms on and within plant surfaces. The screening programme was not only directed at compounds already known to kill or inhibit plant pathogenic bacteria, such as antibiotics or heavy metals (mostly copper), but it was also directed at biological control agents, bacteriophages, antimicrobial peptides, novel chemicals and elicitors. Very few of the products trialled were successful in reducing the incidence of Psa in our experimental conditions. However, from this screening programme streptomycin, kasugamycin, copper-containing compounds and the elicitor Actigard\u2122 (also known as Bion\u2122), which consistently reduced significantly disease incidence, were registered in New Zealand for the control of Psa. Characteristics of some of those compounds, including their potential and limits for control of Psa, will be discussed. One of the interesting results found during this programme was the differential reaction of the green-fleshed Actinidia deliciosa and the yellow-fleshed A. chinensis to some elicitors. To understand the molecular mechanisms involved in the elicitation of resistance by kiwifruit plants, gene expression is being studied in A. chinensis \u2018Zesy002\u2019 (commonly known as Gold3) treated with different elicitor compounds before inoculation with Psa