Heat treatments of dormant scion wood killed the European canker pathogen in planta, while chemical treatments did not

Neonectria ditissima, the causal agent of European canker, can be present in symptomless scion wood. Sanitation treatments could minimise this risk to nursery trees. In this trial, six heat treatments and five chemical treatments were tested for their effectiveness in removing this pathogen from dormant ‘Royal Gala’ wood. In July 2018, 120 symptomless inoculated shoots (three inoculations/shoot) were harvested and stored at 1oC for 3 months. Bundles of five inoculated shoots (45 cm) were placed in the centre of 24 bundles, each consisting of 25 wood pieces. Heat-treated bundles were submerged in water (45oC for 45 min or 50oC for 15 min), or wrapped in moist cloth, vacuum sealed inside plastic then submerged for 3–6 h at the same temperatures. Chemical-treated bundles were submerged for 16 h at room temperature. Treatments were compared with untreated wood. After surface sterilising, isolation of N. ditissima from inoculated wounds was attempted on apple-sap amended water agar. All wounds from the untreated wood and from the chemical-treated wood yielded the pathogen. However, N. ditissima was not isolated from wounds that had been heat treated. Therefore, heat treatments that do not affect scion wood viability may prove an effective tool to remove European canker from nursery material.