Hot water disinfection treatment to eliminate Neonectria ditissima latent infections in apple scion wood

The European canker pathogen, Neonectria ditissima, can be transmitted by apple scion wood into newly developing trees following grafting or budding resulting in disease development and progression. An in vitro hot water treatment showed that both conidia and mycelium of N. ditissima can be killed when placed into water at 50°C for ≥ 5 min. However, diseased scion wood required ≥ 15 min disinfection at the same temperature to eliminate all internal pathogens including N. ditissima. At this temperature and time duration, no mycelium growth was observed after 2 weeks incubation of cut pieces of the disinfected tissues on apple sap amended water agar. Although the treatment was 100% effective at eliminating some identified and non-specific pathogens, visual assessment of both the scion and rootstock viability and vigour six months after the hot water treatment showed that 98% of the rootstocks and scions failed to grow and develop.

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