Agriculture Reference
In-Depth Information
Table 11.1
H
2
S emissions of oilseed rape cultivars differing in susceptibility against
Pyrenopeziza
brassicae
in relation to S fertilisation and growth stage (adapted from Bloem
et al.
, 2007, with permis-
sion from Wiley-Blackwell).
Cultivar
b
Growth stage
c
(BBCH)
Soil-applied S
(kg ha
−1
)
a
H
2
S emission
(pg g
−1
d.w. min
−1
)
0
Genotype 15157
55
−3.4
0
Lion
55
6.2
0
Genotype 15157
65
−4.6
0
Lion
65
0.0
0
Genotype 15157
70
0.8
0
Lion
70
4.6
150
Genotype 15157
55
162.9
150
Lion
55
105.5
150
Genotype 15157
65
26.9
150
Lion
65
14.5
150
Genotype 15157
70
46.3
150
Lion
70
4.0
a
S was applied weekly at rates of 10 kg ha
−1
S during growth before winter and with start of the vegetation period.
b
Lion
rated as resistant, genotype 15157 rated as highly susceptible to
Pyrenopeziza brassicae
.
c
BBCH scale (Strauss
et al.
, 1994).
of fl owering (BBCH 55) when plants had received S regularly since sowing (Table 11.1).
At full fl owering (BBCH 65) and end of fl owering (BBCH 70) plants emitted distinctly
less H
2
S. In comparison, plants that received no S showed very low H
2
S emissions.
Negative values indicate that H
2
S emissions from the soil were greater than from the
plants; no H
2
S was measured in the ambient air. While the cultivar Lion, which is resistant
to the pathogen
Pyrenopeziza brassicae,
showed higher H
2
S emissions when no S was
applied, the susceptible genotype 15157 emitted distinctly higher rates with S fertilisation
(Table 11.1).
No data are available on the infl uence of S supply on phytoalexin synthesis, so any
impact can only be inferred from its infl uence on their precursors.
11.2.3
Fungitoxicity of S metabolites
PR-proteins and low-molecular-weight antibiotics have a proven fungitoxic effect (Smith,
1982; Vidhyasekaran, 1997). The signifi cance of phytoalexins for disease resistance
depends upon the speed and magnitude with which they are synthesised rather than the
selective toxicity or selectivity of elicitation (Ku ´, 1994).
For S
0
, free cysteine and methionine, indirect evidence for their antifungal effect is
given by the fact that concentrations were higher in resistant than non-resistant plant tis-
sues (Cooper
et al.
, 1996; Vidhyasekaran, 2000). A distinct increase in cysteine in host
tissue and emissions of H
2
S was found in the initial phase of pathogenesis (Kruse
et al.
,
2005; Bloem
et al.
, 2007). It might be speculated that enrichment with S
0
affects the
pathogen most in the initial phase of development, after adhesion of conidia and germ
tube formation, but before penetration by appressoria, since Kassemeyer (2003) found
the highest effi ciency of foliar-applied S
0
against powdery mildew of grapes at this stage
of germling development.
