| Dutch elm disease (DED) is a lethal vascular wilt disease, which during the last 100 years has led to a massive mortality of elm trees (Ulmus spp.) in Eurasia and North America, threatening the existence of susceptible elm species over large geographical areas. In Sweden, the disease is known since early 1950s. Subsequently, the incidence and spread of DED gradually increased, in particular during the 1980s when the presence there of aggressive DED-pathogen has been detected.
Since 1986 DED is regarded as a serious threat to Swedish elm population. However, as compared with other areas of Sweden and Europe, to Gotland Island the disease arrived just recently, and for the first time it was observed there only in year 2005. Currentlyt it obviously threatens there the existence of lundalm (Ulmus minor). Population of lundalm in Gotland is unique in its origin, history, development, and ecology. Aim of the project is to understand pathological process of DED in Gotland and to suggest measures for the most effective short- and long-term disease control.
Project objectives are: a) to identify DED pathogens in Gotland; b) to monitor their distribution and spread; c) to determine their genetic population structure; d) to continuously minimize number of DED-infested trees and bark beetles; e) to search for and select DED-resistant elm clones native to Gotland. The project consists of three parts: 1) populations of DED pathogens in Gotland, 2) continuous disease management aimed at eradication; 3) resistance of Gotland elm to DED.
Tasks for part 1: a) sampling DED-infected elms; b) trapping S. multistriatus with pheromone traps; c) pure culture isolations from tree samples and beetles; d) mapping geographic spread of O. novo-ulmi; e) determining the identity (ssp. novo-ulmi , ssp. americana or O. ulmi) and eventual occurrence of their hybrids; f) determining genetic diversity and population structure of Ophiostoma spp. in Gotland.
Tasks for part 2: a) establishing permanent sample plots that include stumps of felled DED-diseased and adjacent “risk trees”, b) applying different Roundup stump treatment regimes on those (e.g., time of the year, time lag since felling and treatment, burning); c) yearly evaluation of treatment effect (e.g., in relation to treatment, stump diameter, location); d) establishing permanent plots with yearly vaccination trials and evaluation on those of tree health condition (in respect to presence of beetle and pathogen); e) continuous monitoring on Gotland of infectiousness of S. multistriatus with O. novo-ulmi (e.g., evaluation of eventual long-term effect of vaccination).
Tasks for part 3: a) field selection of Gotland elms which do not exhibit DED symptoms despite S. multistriatus attacks; b) their clonal propagation; c) replicated pathogenicity tests with DED fungi collected in Gotland.
All necessary expertise, techniques and equipment to carry out planned work are available at the Department of the applicant. The application is strongly supported by Gotland administration. In context of this project, working contacts have been established with the staff of New Zealand Forest Research Institute, that have succesful long-term experience in DED management and control.
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