6 Wood Discoloration

3.7 Restrictions of Physiological Data 77
change of the stem direction, the next hymenia again follow this change.
An exception among the hymenia of following the gravity occurs in the resupinate
fruit bodies of house-rot fungi. The hymenium points upwards in
fruit bodies growing on the floor, and orientates to the side in fruit bodies
growing on a wall. The gravity perception in fungi was investigated by
fruiting experiments with Flammulina velutipes under micro-gravitation condition
during the German D-2 spacelab mission 1993 in the US space shuttle
Columbia (Kern et al. 1991; Fig. 3.3). A positively gravitropic reaction can be
simply demonstrated in the laboratory if a Petri dish with grown mycelium
of a well-fruiting fungus like Schizophyllum commune is upside down for
fruiting.
According to the statolithe theory, amyloplasts and the cytoskeleton in statocyte
cells are involved in gravitropic reactions of plants. Fungi however do
not possess statolithes. Gravity reaction of F. velutipes was hypothesized to
occur as follows: In the case of correct negative gravitropic adjustment of
the fruit body, a mycohormon that is produced in the lamellae is permanently
transported into the upper pileus area. The hormone effects a length
increase on all sides, mediated by the synthesis of vesicles and their following
insert. Incorrect adjustment effects an unequal hormone distribution that influences
vesicle formation and subsequent unilateral stretching growth (Kern
1994).
3.7
Restrictions of Physiological Data
Dataintheliteraturewithrespecttothephysiologyofwoodfungilikegrowth
reactions to environmental factors should be valued with proviso. First, a fungus
may be misnamed due to wrong identification. Thus, DNA-analyses of
closely related house-rot fungi of the genera Antrodia and Coniophora, respectively,
have shown that about 15% of all investigated isolates belonging
to these genera and sampled from own and various other strain collections
were wrongly identified. As extreme, an isolate named A. serialis revealed to
be Donkioporia expansa (Schmidt and Moreth 2003). Second, due to changes
in the taxonomy, there may be considerable confusion in older references, e.g.,
with respect to Antrodia vaillantii and Oligoporus placenta,becausebothhad
been termed Poria vaporaria (Domański 1972). Third, generalizing statements,
like a fungus is faster growing than others, have to be restricted, because there
is considerable strain variation within a species. Table 3.11, based on isolates
that had been verified by rDNA-ITS sequencing, shows as an example for variation
that there are isolates of the so-called “fast-growing” Coniophora puteana
exhibiting a lower growth rate than isolates of the “medium-growing” Antrodia
vaillantii. Fourth, comparisons between different fungi/authors/publications
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