Agriculture Reference
In-Depth Information
H
2
S is described in the literature as being highly fungitoxic (Beauchamp
et al.
, 1984;
Carlile
et al.
, 2004), but no critical values are available for H
2
S concentrations and
duration of fumigation in relation to individual pathogens, which would permit an evalu-
ation of H
2
S emissions of plants with view to their role in SIR. First experiments with
H
2
S fumigation of fungal cultures, however, reveal that its effect is obviously not only
related to concentration and duration of fumigation, but also to the taxonomic group of
the pathogen (Figure 11.2).
Growth of
S. sclerotiorum
was signifi cantly reduced after 24 and 48 hours at all H
2
S
concentrations; only at 10 µl l
−1
H
2
S were differences not signifi cant statistically after
24 hours (Figure 11.2). With increasing H
2
S concentration colony growth of
Rhizoctonia
solani
was signifi cantly inhibited by the time the fumigation was terminated (Figure
11.2). This effect was also observed three and four days later and was consistent for all
durations of fumigation (Yang
et al.
, 2006). An inverse effect of the duration of fumiga-
tion was found in that it signifi cantly promoted colony growth (Figure 11.2). The impact
was greatest immediately after fumigation, with a mean colony diameter that was 80%
higher when the mycelium was fumigated for the longest period of 16 hours (Yang
et al.
,
2006). The effects proved to be consistent for all H
2
S concentrations (Yang
et al.
, 2006).
Basidiomyceta are known to degrade H
2
S and dimethyl sulphide (DMS) by oxidation to
sulphate and dimethylsulphoxide (Phae & Shoda, 1991), so that it might be assumed that
in this taxonomic group of fungal pathogens, H
2
S is not involved in SIR.
Comparing these data with that from H
2
S emissions from plants (Table 11.1), it is
evident that even an excessive S supply might not increase emissions to a level that they
become fungitoxic. However, it is possible that increased H
2
S emissions are concentrated
locally around the site of infection and thus not yet measurable. Riemenschneider (2006),
for instance, has shown that in leaves of
A. thaliana,
H
2
S concentrations of 4-10 µM
could be detected in the mesophyll.
Publisher's Note:
Permission to reproduce this image
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of this chapter.
Figure 11.2
Infl uence of fumigation with rated H
2
S concentrations on growth of mycelia of
Sclerotinia
sclerotiorum
and
Rhizoctonia solani
(adapted from Yang
et al.
(2006) and Haneklaus
et al.
(2007c), with
permisstion from
Phyton
journal).
