Fig. 10.9Dutch elm disease caused by
Ophiostoma ulmiand O. novo-ulmi. (a)
Dying elm trees with thinning crowns.
(b) Coremia of Ophiostoma, consisting
of many aggregated conidiophores,
bearing minute conidia in a large,
sticky mass at the tip (much of this spore
mass was lost during preparation). (c)
Beetle bark galleries on the inside of the
bark; the initial gallery caused by the
adult female is marked, and radiating
from this are galleries produced by the
young larvae. (d) Section of a branch
from a dying elm tree, showing a ring
of blocked, discolored xylem vessels
from a nonlethal attack in a previous
growth season.
(a)(c) (d)(b)Fig. 10.10Dutch elm disease. (a) Diagram of an intact coremium. (b) Sexual stage of Ophiostoma– a long-necked
cleistothecium (closed fruitbody) containing oval asci each containing eight ascospores. The asci break down at maturity
and the ascospores are extruded in mucilage at the tip. (c,d) Beetle brood gallery in the inner bark of a diseased tree.
The adult female beetle deposits eggs along the gallery, then the emerging beetle larvae eat out a series of lateral galleries
ending in chambers. The fungus sporulates in these chambers and contaminates the beetles that emerge in spring.