SECONDARY METABOLITES AND STROMATAL PIGMENTS
Stromatal pigments, or the lack of such pigments,
are useful in delimiting genera in the Xylariaceae (Whalley and Edwards, 1995) and in
delineating taxa in Hypoxylon Bull. (Ju and Rogers, 1996) and in Daldinia
herein. Stromatal pigments are secondary metabolites or are synthesized from them.
Secondary metabolites have not been as widely used as they might be owing to a reputation
for sensitivity to environment and general lack of chemical understanding (Whalley and
Edwards, 1995). The main coloring agents in the Hypoxylon fragiforme
(Pers.: Fr.) J. Kickx fil. teleomorph is said to be mitorubrin (Whalley and Edwards, 1995)
and the same or related compounds are probably to be found in Daldinia.
Whalley and Edwards (1995) cited papers of Allport and Bu'lock dealing with different
secondary metabolites of D.
concentrica from ascomata and from cultures, respectively. Whalley and
Edwards (1995) note that the presence of naphthalene compounds in Entonaema
A. Möller and Daldinia reinforce Rogers' conviction (1982) that these
genera are closely related.
Shigo (1974) has shown that care must be taken with the methodology employed in evaluating pigments. He showed that filtrate and mycelium of D. concentrica is green under standard culturing conditions, but is colorless in media amended with manganese. He conjectured that D. concentrica and some other wound-invading fungi are aggressive wound invaders adapted to high concentrations of minerals that accumulate in tissues as they die, discolor, and decay (Shigo, 1974). The high concentration of minerals may affect pigmentation of some fungi and also the color of the wood (Shigo, 1974).
As will be seen later herein, some stromata of a given species produce extractable pigments and others do not. This is thought to be owing primarily to changes occurring during stromatal aging, but substrate could also be a factor.