Incidence of the emerging pathogen Neonectria neomacrospora on Abies taxa in the National Arboreta in England (UK)

Abstract

In 2008 a severe canker disease of firs (Abies spp.) caused by Neonectria neomacrospora was reported in Norway. In 2011, the same disease was reported in Denmark and, in 2013, it was included in EPPO (European and Mediterranean Plant Protection Organization) Reporting Service as a new emerging disease. In 2015 the disease was detected in England causing dieback on firs. Different studies suggest different susceptibility levels of Abies species to N. neomacrospora. Therefore, the objectives of this study were to investigate the incidence of N. neomacrospora on two of the most important tree collections in England, Bedgebury National Pinetum (BNP) and Westonbirt The National Arboretum (WTNA). Surveys were carried out during January and February 2020. Visual assessment using a health scale from 0 to 10 was carried out on 780 trees comprising 46 different Abies species. Samples were collected from 290 symptomatic trees and isolations were performed in the laboratory to confirm the presence of the pathogen. Identification of the pathogen was confirmed by colony morphology and by real-time PCR. The disease was detected on 32 Abies species. In BNP, N. neomacrospora was isolated from 29% of the sampled trees on 25 different Abies spp., while at WTNA, N. neomacrospora was isolated on 44% of the sampled trees on 18 different Abies species. In total, there were 11 Abies species from which N. neomacrospora was isolated consistently in both BNP and WTNA: A. cephalonica, A. cilicica, A. concolor, A. firma, A. grandis, A. homolepis, A. nordmannniana, A. numidica, A. procera, A. vejarii and Abies × vilmorinii. Additionally, pathogenicity of N. neomacrospora was tested on 400 one-year-old seedlings of eight Abies taxa: A. alba, A. amabilis, A. concolor var. concolor, A. concolor var. lowiana, A. fraseri, A. grandis, A. nordmanniana and A. procera. Neonectria neomacrospora was pathogenic in all species. The largest lesions were detected on A. concolor, A. alba and A. amabilis and disease symptoms differed from species to species. Although N. neomacrospora is present in the tree collections studied, the damage caused by the fungus was not severe and no death of trees was recorded during this survey. However, climate change could play an important role on disease development and trees should be monitored in the future.