Agriculture Reference
In-Depth Information
Bacillus
sp
.
and
Rhodococcus
sp
.
(Gram-positive bacteria) (Saharan and Nehra
2011
) also deprive native microflora from available iron and thus outnumber the
native microbes and exhibit plant growth-promoting effect (Kloepper et al.
1980
).
11.3.2.3
Induced Systemic Resistance
Induced systemic resistance (ISR) is another indirect mode of action where PGPR
or nonpathogenic rhizobacteria act as stimuli, and in response, plants develop
enhanced resistance to pathogens. ISR involves actions of nonpathogenic bacteria
and is mainly dependent on jasmonic acid and ethylene signaling in plants
(Lugtenberg and Kamilova
2009
). Some of the putative mechanisms responsible
for enhanced resistance include accumulation of phenolic compounds, increased
activity of defense enzymes, enhanced lignifications, etc. Many
Pseudomonas
sp
.
and
Bacillus
sp
.
are recognized to act as biocontrol agents and protect plant from
pathogens through this mechanism (Kloepper et al.
2004
). PGPR-mediated ISR
against bacteria, fungi, and viruses has already been reported (Niranjan et al.
2005
).
11.4 Microbial Consortium
“Consortium” is a Latin word, which stands for partnership, association, or group,
that works for common interest. From the microbiological perspective, consortium
constitutes a group of compatible organisms belonging to different species in
contact with one another, implicated in different biological processes ranging
from sewage treatment to metabolic processes in rumen (Mark
2009
). Two or
more microorganisms living in symbiosis can be called as consortium. Microbes
with different attributes can be used as consortium, which can work synergistically
promoting each other's beneficial effects. Some of the PGPR consortium-related
studies are summarized in Table
11.2
. A study involving N
2
fixing,
R. leguminosarum
bv.
viceae
(LB-4); P solubilizing,
B. megaterium
; and PGPR,
LK-786 (
Kurthia
sp.) and LK-884 (
Pseudomonas diminuta
) was carried out to
ascertain their effects on lentil (
Lens culinaris
) crop following single and dual
culture inoculation (Kumar and Chandra
2008
). Maximum increase in dry weight,
yield, mineral uptake, and nodule number was reported in case of all microbial
combination as compared to dual combinations of
Rhizobium+B. megaterium or
Rhizobium+
LK-884/LK-786 (
Kurthia
sp.), whereas no positive effects were
observed in uninoculated controls. A similar study was carried out using consor-
tium of
Burkholderia gladioli
10242,
Enterobacter hormaechei
10240,
Pseudomo-
nas synxantha
10223, and
Serratia marcescens
10241, for their effect on the
Aloe
vera
plants. The result indicated augmented biomass as well as aloin-A content of
the plants (Gupta et al.
2012
). An experimental study was conducted on the
evaluation of effects of PGPR consortium comprising FCA-8, FCA-56, and
FCA-60 of
P. putida
and arbuscular mycorrhizal fungi (AMF) on citrus (
Citrus
