Agriculture Reference
In-Depth Information
11.6.3 Metal Stress
Plant growth-promoting attributes of metal-tolerant
Flavobacterium
sp
.
,
Rhodococcus
sp., and
Variovorax paradoxus
were found to stimulate the root
growth of rapeseed both in the presence and the absence of Cd, supporting their
role as promoters under metal-stressed situation (Belimov et al.
2005
). A study on
the effect of metal-tolerant PGPR
Burkholderia
sp. CMBM40 and
Methylobacterium oryzae
CMBM20 inoculation on tomato plants grown in Ni-
and Cd-treated soil was carried out. The PGPR were found to decrease the metal
uptake by plants and also enhanced the plant growth by producing growth hor-
mones (Madhaiyan et al
.
2007
). Consortia of
Bradyrhizobium
sp. with metal-
tolerant PGPR
Pseudomonas
sp. and
Ochrobactrum cytisi
significantly improved
biomass, yield, and N content of metal accumulating
Lupinus luteus
plants but they
decreased metal accumulation within plants (Dary et al.
2010
). Likewise, the metal-
tolerant PGPR consortia significantly increased root length, shoot length, biomass,
and chlorophyll content of mung bean by 138 %, 88 %, 256 %, and 54.1 %,
respectively, when grown in chromium-treated soils (Singh et al.
2010
). Similar
enhancement in some cereals, for example, wheat following metal-tolerant PGPR,
B. thuringiensis
and
P. fluorescens
(Shahzadi et al.
2013
) and
A. brasilense
and
A. chroococcum
(Janmohammadi et al.
2013
), has been reported. The PGPR
Ralstonia eutropha
(B1) and
Chryseobacterium humi
(B2) inoculated sunflower
(
Helianthus annuus
) plants when grown in Zn- and Cd-contaminated soil had
decreased metal concentration inside plant tissues, suggesting that metal-resistant
PGPR might have served as effective stabilizers for plants grown in metal-
contaminated soil (Marques et al.
2013
).
11.7 Conclusion
Among various abiotic stresses, drought, salinity, and metal pollution are the most
stronger and stringent ones, which restrict the overall performance of plants grow-
ing in such derelict soils. The sole or composite (consortia) application of PGPR is
an emerging area of interest because these microbes have been found to enhance the
growth and development of plants both under conventional and stressed environ-
ments in different production systems across varying ecological niches. Moreover,
microbial inoculation is cost effective, environmentally friendly, and easy option
for farm practitioners. However, before they are made commercially available,
more field trials are needed to get the full benefit of this strategy in combating
stress-related problems caused to agronomically important crops. Considering the
available information, it is believed that the practice of PGPR consortium appli-
cation is likely to grow faster and agricultural practices will slowly be able to
shifting its focus from fertilizer to efficacious use of PGPR.
