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 of Ophiostoma 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 of O. ulmi, no hyphae could be found until 5 days after inoculation. However, when U. 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.

A study of the development of Ophiostoma ulmi in elms with immunological techniques

“…As with earlier examinations with the scanning electron microscope (Miller and Elgersma, 1976) we were unable to find direct cell wall penetration, These results are also in agreement with the observations made by Pomerlau (1970).…”

“…Special attention was paid to the possible growth of O. ulmi into parenchyma cells, ray cells or fibres. Because the observation of the fungus within elm wood is difficult (Miller and Elgersma, 1976) inoculations were done with a high concentration of conidia (1.6 x l0 s conidia per ml) of O, ulrni strain E2. distilled water and mounted in polyvinylpyrrolidone.…”

“…by using the light microscope (Ouellette, 1960;Wilson, 1965;Banfield, 1968;Pomerleau, 1970), the transmission electron microscope (MacDonald and McNabb, 1970;Krause and Wilson, 1972) or the scanning electron microscope (King et al, 1974;Miller and Elgersma, 1976). It is still disputed whether the fungus remains confined to the lumina of the xylem vessels during pathogenesis or is also able to invade the surrounding parenchyma cells, ray cells or fibres.…”

Production of pectic and cellulolytic enzymes by aggressive and non-aggressive strains of Ophiostoma ulmi

“…390, than does the nonaggressive strain (Miller and Elgersma, 1976). Obviously, the resistance mechanisms as described by Elgersma (1970Elgersma ( , 1973 do not operate effectively enough to limit the spread of the aggressive strain.…”

Tylose formation in elms after inoculation with an aggressive or a non-aggressive strain of Ophiostoma ulmi or with a nonpathogen to elms

“…As no significant differences appear to exist between the tyloses induced by O. ulmi strains E2 and H6 in clone 390, we must assume that a bypassing of obstacles such as tyloses is probable. This was suggested by Miller and Elgersma (1976) as being due to a more rapid growth and penetration of the vessel pits by the aggressive strain. …”