The growth of aggressive and non-aggressive strains of Ophiostoma ulmi in susceptible and resistant elms, a scanning electron microscopical study

Abstract

Different wood preparation techniques for a SEM study of the growth ofOphiostoma ulmi (Buisman) Nannf. in elm tissue were compared. Critical point drying appeared to be the most suitable method. All observations were made 10–14 cm above the site of inoculation. In the resistant elm,Ulmus hollandica cl. 390, inoculated with a non-aggressive strain ofO. ulmi, no hyphae could be found until 5 days after inoculation. However, whenU. hollandica cl. 390 was inoculated with the aggressive strain, the fungus could already be observed after 3 days. In the susceptible elm,U. hollandica cl. Belgica, whether inoculated with an aggressive or non-aggressive strain, hyphae were found within 2 days after inoculation. The fungus appears only to penetrate the vessel pits and has at no time been seen to penetrate the cell wall directly.