Identification, detection and eradication of Hymenoscyphus fraxineus from ash (Fraxinus excelsior) seeds

The European and Mediterranean Plant Protection Organization (EPPO) real-time PCR protocol for the detection of ash dieback (Hymenoscyphus fraxineus (T. Kowalski) Barak, Queloz, Hosoya) was optimized for diagnostics on ash (Fraxinus excelsior L.) fruits. Ash fruits were collected from a range of sites in Britain, from trees with various levels of infection. To assess the potential pathway and the presence of H. fraxineus, tissue components of ash fruits as well as ash flowers were tested for the presence of H. fraxineus DNA and RNA. The fungus was detected on ash fruits from trees on all five sampled sites including symptomless, lightly and highly infected sites. DNA of H. fraxineus was detected on the pericarps of all fruit lots and on seeds from fruit lots that included damaged and empty fruits, but not on embryos or flowers. RNA of H. fraxineus was never detected on any of the samples or sample types, indicating that H. fraxineus was only detected in an inactive form (i.e. dormant or dead). The absence of RNA from the pathogen suggests that only spores of H. fraxineus are present on ash fruits. A double hot-water treatment was evaluated as a control measure for the eradication of H. fraxineus on ash fruits; these were treated before and after warm stratification. Large proportions of ash fruits survived the double hot-water treatments, with a 60.4 +/- 28.4 per cent germination success rate depending on crop year. Double hot-water treatment of ash fruits proved to be an efficient, low cost and low-tech approach for the eradication of H. fraxineus on ash fruits.