The potential for beneficial microbes and elicitors to reduce damage from Psa disease

This collaborative project is evaluating the potential for beneficial microbes and elicitors to reduce damage to kiwifruit from Psa disease. The project includes foliar application of selected candidate micro-organisms and elicitors, root inoculation with Trichoderma endophytes, root treatment with elicitors and combination treatments. Assays have been developed using kiwifruit seedlings challenged with Psa by stab-wounding the stem or spraying. Systemic plant responses, wound protection, protectant activity of biological control agents (BCAs), elicitors and natural products against Psa are being assessed. Elicitor treatments, mixtures of BCAs spray-applied to the shoot, and several Trichoderma root endophytes have shown promise in reducing Psa in seedling assays and will be tested in Psa-infected orchards. Trichoderma root endophytes have reduced nursery and plantation diseases (by 25–60%) and have increased plant growth (by 5–15%) in New Zealand and South East Asia. The best root endophytic Trichoderma strains have become „standard operational practice‟ for sustainable plantation forestry in the Planted Forest Zone of Malaysian Borneo

The potential for beneficial microbes and elicitors to reduce damage from Psa disease

This collaborative project is evaluating the potential for beneficial microbes and elicitors to reduce damage to kiwifruit from Psa disease. The project includes foliar application of selected candidate micro-organisms and elicitors, root inoculation with Trichoderma endophytes, root treatment with elicitors and combination treatments. Assays have been developed using kiwifruit seedlings challenged with Psa by stab-wounding the stem or spraying. Systemic plant responses, wound protection, protectant activity of biological control agents (BCAs), elicitors and natural products against Psa are being assessed. Elicitor treatments, mixtures of BCAs spray-applied to the shoot, and several Trichoderma root endophytes have shown promise in reducing Psa in seedling assays and will be tested in Psa-infected orchards. Trichoderma root endophytes have reduced nursery and plantation diseases (by 25–60%) and have increased plant growth (by 5–15%) in New Zealand and South East Asia. The best root endophytic Trichoderma strains have become „standard operational practice‟ for sustainable plantation forestry in the Planted Forest Zone of Malaysian Borneo

Developing and using bioassays to screen for Psa resistance in New Zealand kiwifruit

The bacterial pathogen Pseudomonas syringae pv. Actinidiae (Psa), biovar 3 causes a destructive disease of kiwifruit. Psa was first identified in New Zealand on 5 November 2010 on Actinidia chinensis 'Hort16A' (Zespri Gold) kiwifruit vines in the Te Puke region and has now spread to 81% of kiwifruit orchards. Intensive spray programmes based upon Actigard® and copper-based products have been implemented by growers, but the high usage of copper products is unsustainable. Therefore, breeding new cultivars with greater resistance to Psa has become a priority. Plant and Food Research (PFR) has developed a range of bioassays to characterise kiwifruit germplasm (e.g., tissue culture plantlets, potted seedling and mature vines) for resistance to Psa. The 'woody-stem bioassay' measures Psa lesion development and bacterial proliferation on wound-inoculated cane segments (bud wood). The measurements are combined to provide a woody stem bioassay index (WSBI) which ranges from 0 (resistant) to 100 (susceptible). Since its deployment in July 2012, the woody-stem bioassay has been successfully used to determine the Psa resistance status of five commercial cultivars, 75 pre-commercial clonal selections and >2,000 parental and seedling kiwifruit from the PFR breeding programme. A 'green stem-stab' bioassay was also developed to compare susceptibility of actively growing shoots. Soft stems or shoots are inoculated using a toothpick dipped in Psa suspension and then scored for a range of symptoms (e.g. lesion size and stem collapse) after 2-3 weeks incubation in high humidity. This bioassay has been used to evaluate the Psa-resistance status of seedlings from selected crosses, including populations being interrogated for molecular markers of Psa resistance. Seedlings from inter specific-crosses (A. chinensis × A. arguta) exhibited greater resistance to Psa than A. chinensis × A. chinensis seedlings. These bioassays are currently being utilised for identifying genotypes within the PFR kiwifruit breeding programme that are resistant to Psa