Agriculture Reference
In-Depth Information
Table 5.9. Effect of seed treatment with non-pathogenic
Fusarium oxysporum
on fusarium wilt
in chickpea sown in soil infested with
F. oxysporum
f.sp.
ciceris
(from Hervas
et al
., 1997)
Cultivar
F. oxysporum
concentration
(chamydospores
g
-1
soil)
Seed treatment
Disease assessment
Incubation
period
Disease
intensity
Area under
the disease
progress
curve
ICCV 4
500
Non-pathogenic
Fusarium
46.8
20.5
0.07
500
Control
35.4
73.7
0.32
1000
Non-pathogenic
Fusarium
29.7
100.0
0.61
1000
Control
28.3
97.9
0.39
PV 61
500
Non-pathogenic
Fusarium
46.5
4.3
0.01
500
Control
21.7
75.2
0.36
1000
Non-pathogenic
Fusarium
30.3
90.8
0.45
1000
Control
20.0
89.6
0.50
More detailed analyses of dose-response relationships in the amounts of pathogenic
and non-pathogenic soil microorganisms and disease incidence levels, suggest that it
is possible to differentiate between biological control agents that act via induced
resistance and those that are effective as competitors for nutrients even though the
end result, lower disease, may be the same. Such a relationship, involving non-
pathogenic
Fusarium
species, against
Fusarium
wilt of tomato (Larkin and Fravel,
1999) has shown that the resistance-inducing microorganisms are effective at much
lower doses than the competitors. This was reflected in the consequent impact on
overall disease incidence, with inducing agents causing a greater reduction in the
disease level compared to the competitors.
Jørgensen,
et al
. (1998) elegantly described the quantitative ability of the non-
barley pathogens,
Bipolaris
maydis
and
Stagonospora
(
Septoria)
nodorum
to induce
resistance in barley against
Drechslera teres
. Relative to a control pre-treatment with
water, pre-treatment with both non-pathogens reduced the percent conidia forming
appressoria, the percent conidia causing penetrations, the percent conidia forming
intracellular hyphae and the percent conidia causing fluorescent epidermal cells. The
percent conidia causing fluorescent papillae was increased. The enhancement of
resistance was associated with an early defense reaction characterized by the increase
in fluorescent papillae formation, and a late defense reaction linked to multicellular
hypersensitive responses. The authors provided evidence in these induced responses
for the expression of defense response genes that are involved in barley attacked by
powdery mildew.
