Agriculture Reference
In-Depth Information
nutrient uptake was also observed in the bacterized plants, when compared to
uninoculated controls. Very recently, phytase-producing CT-PSB, able to mineral-
ize P
o
as well as to solubilize P
i
, were isolated from Himalayan soil samples
collected at Uttarakhand region, northern India (Kumar et al.
2013
). The isolates
were identified as
Achromobacter
sp. PB-01 and
Tetrathiobacter
sp. PB-03, both
members of the Burkholderiales, and
Bacillus
sp. PB-13. Despite growing at a wide
range of pH (5-11 pH units), temperature (10-42
C), and salt concentrations (from
0 to 8.5 % NaCl), these strains also exhibited diverse PGPR activities, such as
production of IAA and siderophores. Their PGP abilities were confirmed using
Indian mustard as test crop grown under greenhouse conditions at 20-25
C.
Bacterization of seeds with
Tetrathiobacter
sp. PB-03 and
Bacillus
sp. PB-13
significantly increased the biomass and P content of 30-day-old plants. Also,
Tetrathiobacter
sp. PB-03 and
Bacillus
sp. PB-13 inhibited the growth of the
phytopathogen
Rhizoctonia solani
.
Recently, Berrıos et al. (
2013
) used an Antarctic bacterial strain to promote
growth and development of Antarctic hair grass (
Deschampsia antarctica
). The
Pseudomonas
sp. Da-bac TI-8 strain, previously isolated from the rhizosphere of
D. antarctica
, naturally growing in the Antarctic Peninsula (Barrientos-D´az
et al.
2008
), grows both at 4
C and 20
C (doubling times of 4.31 h and 1.31 h,
respectively) but not at 30
C. Even though it grew slower at 4
C, the biomass yield
at the end of the exponential phase in LB medium was almost the same as that
recorded at 20
C. Its P-solubilizing activity at 4
C, attributed to gluconic acid
production, was demonstrated in the presence of calcium phosphate dehydrate,
calcium hydrogen phosphate, and phosphate rock. When
D. antarctica
seedlings
were inoculated with strain Da-bac TI-8, a significant effect on the shoot dry
weight/root dry weight ratio of plants was recorded at 22
C—but not at 13
C—
as compared to uninoculated controls. Interestingly,
Pseudomonas
sp. Da-bac TI-8
was included in the formulation of a microbial bioinoculant developed to efficiently
solubilize P at low temperatures and which was submitted to the US Patent and
Trademark Office (Gidekel et al.
2010
).
5.6.2 Cold-Tolerant Fungi (CTF)
Among the P-solubilizing microorganisms, filamentous fungi occupy a prominent
position. Indeed, some fungal species belonging to
Aspergillus
and
Penicillium
genera have been shown to exhibit high P-solubilizing activities. As in the case of
PSB, release of organic acids (e.g., citric, gluconic, lactic, oxalic, and succinic) is
the main mechanism responsible for this solubilization (Khan et al.
2010
). Besides,
fungi produce larger amounts of organic acids than bacteria and consequently
generally exhibit greater P-solubilizing activities. For example, under certain cul-
ture conditions,
A. niger
can convert glucose to citric acid with more than 80 %
efficiency and at final concentrations of hundreds of grams per liter (Magnuson and
Lasure
2004
). Some other advantages in using fungi, instead of bacteria, for
