6 Wood Discoloration

3.8 Competition and Interactions Between Organisms 85
Investigations have been performed to regenerate the decreased mycorrhizal
occurrence and the species change in forest damage sites by artificial
inoculation and thus to improve the health of these trees and also of trees on
other problematic sites (Römmelt et al. 1987; Marx 1991; Schmitz 1991; Lelley
1992; Hilber and Wüstenhöfer 1992; Schmitz and Willenborg 1992; Göbl 1993;
Kutscheidt and Dergham 1997). However, it has to be considered that thereby
one intervenes only at the symptoms of the damage and not at its causes, that
is, new inoculations without reduction of the emissions might be unsuccessful
in the long run. To improve the isolate characteristics of mycorrhizal species,
interstock matings have been done e.g., with Paxillus involutus (Strohmeyer
1992).
A further association of mutual benefit is lichens, a close and stable partnership
between Ascomycetes (and rarely Basidiomycetes) with green algae
or cyanobacteria (Kappen 1993). In the mutualistic form of lichens, the fungi
receive organic nutrients and vitamins from the algae/bacteria and these get
water and inorganic salts from the fungi. The association allows the pioneer
settlement of inhospitable biotopes such as rocks with only traces of nutrients.
In the antagonistic form, the fungi are parasitic to the algae, and the algae
survive by increasing faster than they are destroyed by the fungi (Schubert
1991). With respect to classification, the lichens are placed in the fungal system
as lichenized fungi.
Fungal associations with animals are the endosymbioses in the mycetomes
of insects. Ectosymbioses occur in the “fungal gardens” of termites and in the
cultivation of the ambrosia fungi in the drill ducts of bark beetles (Francke-
Grosman 1958; Werner 1987). For example, Ips typographus is associated
with ophiostomatoid fungi (Solheim 1999; Sallé et al. 2005). The fungi are
transferred to the tree during the beetle attack and are considered important
partners in beetle population establishment. In addition, fungi invade the
host’s phloem and sapwood, where the hyphae can cause blue stain. Recently,
a symbiosis between three partners was found: leaf cutter ants in Panama and
Ecuador are associated with a basidiomycete fungus, but additionally with
abacterium(Streptomyces sp.) which was shown to be antagonistic against
a parasitic ascomycete that has a negative effect on the ant/basidiomycete interaction
(Anonymous 1999). Aspects of the association of fungi and insects
with the infected trees are described by Raffa and Klepzig (1992).
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