Agriculture Reference
In-Depth Information
physiology and metabolic responses, leading to an enhanced synthesis of plant
defense chemicals upon challenge by pathogens and/or abiotic stress factors
(Ramamoorthy et al.
2001
; Nowak and Shulaev
2003
; Alizadeh et al.
2013
). Inter-
estingly, the rhizobacteria-assisted ISR is identical to that of pathogen-induced
SAR in that both types of induced resistance make uninfected plant parts more
resistant to a broad spectrum of plant pathogens. The type of bioprimed plant
response induced after challenge with a pathogen results in the formation of
structural barriers, such as thickened cell wall papillae due to the deposition of
callose and the accumulation of phenolic compounds at the site of pathogen attack
(Benhamou et al.
1996a
,
1998
). Similarly, biochemical or physiological changes in
plants following inoculation include induced accumulation of pathogenesis-related
proteins (PR proteins) such as PR-1, PR-2, chitinases, and some peroxidases
(Viswanathan and Samiyappan
1999
; Park and Kloepper
2000
; Jeun et al.
2004
;
Latha et al.
2009
; Raj et al.
2012
; Chowdappa et al.
2013
). However, certain PGPB
do not induce PR proteins (Hoffland et al.
1995
; Pieterse et al.
1996
; Van Wees
et al.
1997
); instead, it increases the accumulation of peroxidase, phenylalanine
ammonia lyase, phytoalexins, polyphenol oxidase, and/or chalcone synthase (Van
Peer et al.
1991
; Ongena et al.
2000
; Chen et al.
2000
; Ramamoorthy et al.
2001
;
Chowdappa et al.
2013
). In several studies, numerous rhizobacteria have been
found to trigger the salicylic acid (SA)-dependent SAR pathway by producing SA
at the root surface, whereas some other rhizobacteria triggered different signaling
pathway independent of SA. The SA-independent ISR pathway has been observed
in
Arabidopsis thaliana
, which is dependent on jasmonic acid (JA) and ethylene
signaling. Similar ISR in plants, for example, carnation, cucumber, radish, tobacco,
and
Arabidopsis
following
Pseudomonas
inoculation, is reported (Choudhary
et al.
2007
). In addition to
Pseudomonas
strains, ISR is developed following
inoculation of different
Bacillus
species, for example,
B. amyloliquifaciens
,
B. subtilis
,
B. pasteurii
,
B. cereus
,
B. pumilus
,
B. mycoides
, and
B. sphaericus
,
and shown considerable reduction in the incidence or severity of various diseases
on a variety of hosts (Choudhary et al.
2007
). Similarly, the ISR in one of the study
was triggered by
Trichoderma harzianum
Tr6 and
Pseudomonas
sp. Ps14, both
isolated from the rhizosphere of cucumber, and had inhibitory activity against
Fusarium oxysporum
fsp.
radicis cucumerinum
(cucumber) and in
A. thaliana
against
Botrytis cinerea
(Alizadeh et al.
2013
). In other reports, the ISR was
triggered by
P. fluorescens
(Pf1 and Py15) and
B. subtilis
(Bs16) when used either
alone or together and as mixture with the most effective plant extract, Zimmu, in
both in vitro and in vivo experiments against early blight disease in tomato caused
by
A. solani
(Latha et al.
2009
),
P. fluorescens
EP1 against red rot caused by
Colletotrichum falcatum
on sugarcane (Viswanathan and Samiyappan
1999
),
Burkholderia phytofirmans
PsJN against
Botrytis cinerea
on grapevine (Barka
et al.
2000
,
2002
),
Verticillium dahliae
on tomato,
P. denitrificans
and
P. putida
against
Ceratocystis fagacearum
on oak (Brooks et al.
1994
),
P. fluorescens
against
F. oxysporum
fsp.
radicis-lycopersici
on tomato,
B. pumilus
SE34 against
F. oxysporum
fsp.
pisi
on pea roots (Benhamou et al.
1996b
), and
F. oxysporum
fsp.
vasinfectum
on cotton roots (Conn et al.
1997
). Recently,
B. pumilus
strain
