Agriculture Reference
In-Depth Information
9.8.2 MECHANISMS THAT MEDIATE PATHOGEN SUPPRESSION
Two possible mechanisms of pathogen suppression have been described,
one depends on systemic plant resistance and the other is mediated by
microbial competition, antibiosis and hyperparasitism (Hoitink and Gre-
bus 1997). The microbially mediated suppression is again classified into
two mechanisms viz., 'general suppression' where a wide range of mi-
crobes suppress the pathogens such as
Pythium
and
Phytopthora
(Chen
et al. 1987) and 'specific suppression' where a narrow range of organ-
isms facilitates suppression, for instance disease caused by
Rhizoctonia
(Hoitink et al. 1997). The disease suppressive effect of vermicompost
against fusarium wilt of tomato clearly depicted that fungus inhibition
was purely biotic and no chemical factors played any role, since the ex-
periments with heat-sterilized vermicompost failed to control the disease
(Szczech 1999). Experiments on suppression of damping-off caused by
R. solani
, in vermicompost amended nurseries of white pumpkin proved
that vermicompost suppressed the disease in a dosage and temperature
dependent manner (Rivera et al. 2004). Earthworm castings are rich in
nutrients (Lunt and Jacobson 1944; Parle 1963) and calcium humate, a
binding agent (Edwards 1998) that reduces desiccation of individual cast-
ings and favors the incubation and proliferation of beneficial microbes,
such as
Trichoderma
spp. (Tiunov and Scheu 2000),
Pseudomonas
spp.
(Schmidt et al. 1997), and mycorrhizal spores (Gange 1993; Doube et al.
1995). Earthworm activity increased the communities of Gram-negative
bacteria (Clapperton et al. 2001; Elmer 2009). Vermicompost associated
chitinolytic bacterial communities viz.,
Nocardioides oleivorans,
several
species of
Streptomyces
and
Staphylococcus epidermidis
showed inhibi-
tory effects against plant phytopathogens such as,
R. solani, Colletotri-
chum coccodes, Pythium ultimum, P. capsici
and
Fusarium moniliforme
(Yasir et al. 2009a).
9.9 ROLE OF VERMICOMPOST IN ARTHROPOD PEST CONTROL
Addition of organic amendments helped in suppression of various insect
pests such as European corn borer (Phelan et al. 1996), other corn
