Agriculture Reference
In-Depth Information
there is a direct link between ethylene and the auxin response and that this study
provides more evidence for the stress-reducing benefits of ACC deaminase-
expressing plant growth-promoting bacteria (Stearns et al. 2012 ).
10.3.2
Indirect Plant Growth Promotion Through Induced
Systemic Resistance
Inoculation of plants with sole or multiple plant growth-promoting activities
containing PGPR including PS bacteria is reported to provide systemic resistance
against a broad spectrum of plant pathogens, for example, those belonging to
fungal, bacterial, and viral groups (Ryu et al. 2004b ; Latha et al. 2009 ; Raj
et al. 2012 ; Alizadeh et al. 2013 ; Son et al. 2014 ).
10.3.2.1
Induced Systemic Resistance
Plants have numerous active defense apparatuses that can aggressively be
expressed when exposed to biotic stresses such as phytopathogens and parasites
or viruses to phytophagous insect. Induced systemic resistance (ISR) is a phenom-
enon in plants which is triggered principally following inoculation of microbial
cultures and is phenotypically similar to the systemic acquired resistance (SAR)
that occurs when plants activate their defense systems in response to infection by a
pathogenic agent (Pieterse et al. 2009 ). Induced systemic resistance of plants
against pathogens is a widespread phenomenon that has its potential use in the
management of phytopathogens, for instance, fungi, bacteria, and viruses. Induced
systemic resistance involves jasmonate (JA), ethylene, and salicylic acid
(SA) signaling within plants, and these hormones stimulate the host plant's defense
responses to a range of pathogens (Verhagen et al. 2004 ). Besides ethylene, JA, and
SA, other bacterial molecules such as the O -antigenic side chain of the bacterial
outer membrane protein lipopolysaccharide, flagellar proteins, pyoverdine, chitin,
β
-glucans, and cyclic lipopeptide surfactants have been reported to act as signaling
molecules inducing ISR. However, ISR does not require any direct interaction
between the resistance-inducing bacteria and the pathogens (Bakker et al. 2007 ).
Strains of PGPR are reported to suppress diseases by antagonism between the
bacteria and soilborne pathogens (Khan et al. 2002 ) and by ISR in plants against
pathogens (Beneduzi et al. 2012 ; Alizadeh et al. 2013 ). The PGPB-elicited ISR was
first observed on carnation ( Dianthus caryophillus ) with reduced susceptibility to
wilt caused by Fusarium sp. (Van Peer et al. 1991 ) and on cucumber ( Cucumis
sativus ) with reduced susceptibility to foliar disease caused by Colletotrichum
orbiculare (Wei et al. 1991 ). Manifestation of ISR is dependent on the combination
of both host plants and bacterial strains (Van Loon et al. 1998 ; Kilic-Ekici and Yuen
2004 ). The bacterial triggered ISR strengthens plant cell wall and alters host
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