Agriculture Reference
In-Depth Information
A. niger
,
A. flavus
,
F. oxysporum
,
A. alternata
,
C. arachichola
,
M. anisopliae
, and
P. solanacearum
(Sayyed and Patel
2011
). However, the control preparation (free
of any siderophore activity) did not inhibit the growth of any of the test fungal
species consolidating the role of siderophores in disease suppression. Rhizobacteria
capable of synthesizing and releasing siderophores are also known to be involved in
inducing systemic resistance (ISRs) to the plants (Wees et al.
2000
; Pieterse
et al.
2001
) and suppressiveness to the soil (Mazzola
2002
). Summarily, the
siderophore-based biological control agents must be popularized among field
practitioners for reasons as they (1) are inexpensive and nondestructive (safer) to
the environment, (2) are self-replicating in the environment and hence do not
require repeated application, (3) do not lead to biomagnification, and (4) have no
emergence of resistance among target organisms (Sayyed et al.
2005
).
Antibiosis
Antibiotics are bioactive microbial metabolites that at low concentrations inhibit
the growth or metabolic activities of other organisms (Thomashow and Weller
1995
). Microbial communities able to produce antibiotics are common in natural
environment. Historically, the natural antibiotics are reported to contribute to
(1) microbial defense, (2) fitness, (3) interference, and (4) competitiveness (Wise-
man et al.
1996
; Haas and Defago
2005
; Mavrodi et al.
2006
; Fajardo and Martinez
2008
; Little et al.
2008
). The antibiotic-mediated inhibition of plant pathogens by
rhizosphere-inhabiting biocontrol microorganisms is well documented
(Raaijmakers et al.
2002
; Haas and Keel
2003
; Haas and Defago
2005
; Raaijmakers
and Mazzola
2012
). Among all the PGPR strains,
Bacillus
and
Pseudomonas
are
the two most common genera widely used in the disease management practices
through antibiotics production. Perhaps, a well-known example is the suppression
of take-all disease in wheat by 2,4-diacetylphloroglucinol, produced by
P. fluorescens
in the rhizosphere (Weller et al.
2007
). However, like many other
bacterial species, the antibiotics production by PS organisms is also one of the
important traits by which the PS bacteria prevent the proliferation of plant patho-
gens (Sunish et al.
2005
; Naik et al.
2008
; Mazurier et al.
2009
). Since then, a
variety of antibiotics have been identified, including compounds such as amphisin,
2,4-diacetylphloroglucinol (DAPG), oomycin A, phenazine, pyoluteorin,
pyrrolnitrin, tensin, tropolone, and cyclic lipopeptides produced by pseudomonads
(Defago
1993
; Nielsen and Sørensen
2003
; Raaijmakers and Mazzola
2012
; Zhou
et al.
2012
; Saraf et al.
2014
) and oligomycin A, kanosamine, zwittermicin A, and
xanthobaccin produced by
Bacillus
,
Streptomyces
, and
Stenotrophomonas
spp.
(Milner et al.
1995
,
1996
; Hashidoko et al.
1999
; Nakayama et al.
1999
; Mavrodi
et al.
2012
). In a study, 2,4-diacetylphloroglucinol (DAPG) and pyoluteorin (PLT)
producing
P. fluorescens
CHA0 promoted the growth of various plants and
protected them against root diseases caused by pathogenic fungi. Among the
organic acids, gluconic acid was the principal acid produced by
Pseudomonas
spp. and the mutant strain (genes encoding glucose dehydrogenase (
gcd
) and
