Strong in vitro antagonism by elm xylem endophytes is not accompanied by temporally stable in planta protection against a vascular pathogen under field conditions
- 424 Downloads
Some endophytic fungi provide their host plants with protection against abiotic and biotic stressors, including pathogens. Endophyte-mediated mechanisms might be behind the environmental resistance shown in the field by some adult Ulmus minor trees to the Dutch elm disease (DED) pathogen, Ophiostoma novo-ulmi. We isolated and characterized seven endophyte fungi from the xylem of three adult U. minor trees that have survived the DED epidemics within areas in Spain ravaged by the disease. The antagonism of the isolated endophytes towards O. novo-ulmi was evaluated in vitro by means of dual culture assays. Six of the studied endophytes hindered the pathogen growth through antibiosis, competition for the substrate, or a combination of both mechanisms. Four of these endophytes were selected for in vivo tests where their protective effect was evaluated in field experiments during three successive years (2011–2013). The conditioning inoculation of two endophytes (Monographella nivalis and Alternaria tennuissima) reduced DED symptoms in 2011 and 2012, respectively. However, the same isolates did not show any prophylactic effect in 2013, which suggests that the repeatability of the treatments is low. A significant treatment × clone interaction was found, showing that the effectiveness of the treatments depended on the tree clone. The future use of endophytes in biocontrol strategies might be oriented towards taking into consideration the whole fungal microbiome in forest breeding programs rather than the external application of particular endophyte strains.
KeywordsEndophytes Dutch elm disease Ophiostoma novo-ulmi Tree resistance Ulmus
- AEMET (State Meteorology Agency of Spain) (2015). Monthly climate reports. http://www.aemet.es/es/portada. Accessed 7 January 2015.
- Blumenstein, K. (2010). Characterization of endophytic fungi in the genus Ulmus: putative agents for the biocontrol of Dutch Elm Disease (DED). Diploma thesis, University of Kassel, 114 p.Google Scholar
- Hubbes, M. (2004). Induced resistance for the control of Dutch elm disease. Forest Systems, 13, 185–196.Google Scholar
- Kais, A., Smalley, E., & Riker, A. (1962). Environment and development of Dutch elm disease. Phytopathology, 52, 1191–1196.Google Scholar
- Martín, J. A., Solla, A., Buron, M., Lopez-Almansa, J. C., & Gil, L. (2006). Historical, ecological, taxonomic and health characterization of the relict elm stand of Rivas-Vaciamadrid (Madrid). Forest Systems, 15, 208–217.Google Scholar
- Ouellette, G. B., Rioux, D., Simard, M., & Cherif, M. (2004). Ultrastructural and cytochemical studies of host and pathogens in some fungal wilt diseases: retro- and introspection towards a better understanding of DED. Forest Systems, 13, 119–145.Google Scholar
- Scheffer, R. J., Elgersma, D. M., De Weger, L. A., & Strobel, G. A. (1989). Pseudomonas for biological control of Dutch elm disease. I. labelling, detection and identification of Pseudomonas isolates injected into elms: comparison of various methods. Netherlands Journal of Plant Pathology, 95, 281–92.CrossRefGoogle Scholar
- Solla, A., Dacasa, M. C., Nasmith, C., Hubbes, M., & Gil, L. (2008). Analysis of Spanish populations of Ophiostoma ulmi and O. novo-ulmi using phenotypic characteristics and RAPD markers. Plant Pathology, 57, 33–44.Google Scholar
- White, T. J., Bruns, T., Lee, S., & Taylor, J. W. (1990). Amplification and direct sequencing of fungal ribosomal RNA genes for phylogenetics. In M. A. Innis, D. H. Gelfand, J. J. Sninsky, & T. L. White (Eds.), PCR protocols: A guide to methods and applications (pp. 315–322). New York: Academic.CrossRefGoogle Scholar