“RHIZOSPHERE BACTERIAL COMMUNITY AND ACTIVITY IN LOW PHOSPHORUS TOLERANT RICE GENOTYPES”
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Date
2019
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PROFESSOR JAYASHANKAR TELANGANA STATE AGRICULTURAL UNIVERSITY
Abstract
Rice is one of the most important crop in the world. However, its production
is largely limited by the phosphorus (P) deficiency in many soils. Developing
cultivars with tolerance to low P represents a sustainable solution to the problem of
rising P fertilizer cost and diminishing natural P resources.
The present investigation was carried out to study the interactions between
plant root and rhizosphere microflora and their activities of rice genotypes differing
in their response to low available phosphorus in soil. The effect of genotypes Rasi,
Wauzhopek, Swarna, PUP 244, PUP 236, ISM and MTU1010 on microbial
population, diversity, soil microbial biomass phosphorus (SMBP) and soil enzyme
activities were studied in relation to plant growth and phosphorus uptake.
Significantly higher population of bacteria, fungi, actinomycetes and
phosphate solubilising bacteria (PSB) were supported in the rhizosphere of PUP 244
at maximum tillering, flowering and at harvest. At flowering, the critical stage that
generally supports the highest microbial activity in rhizosphere, PUP 244 recorded
highest population of bacteria, fungi, actinomycete and PSB (7.46, 4.83, 5.71 and
6.88 log CFU g-1
soil respectively) while comparatively lower populations were
recorded in rhizosphere soils of MTU 1010 (7.26, 4.38, 5.01 and 6.32 log CFU g-1
soil respectively). The genotype Rasi was found to support greater number of
bacterial morphotypes (25) in the rhizosphere, and displayed the highest Shannon
diversity index of 1.06 and the evenness of 0.76. This was followed by ISM and
Wauzhopek. Unique bacterial morphotypes (161) isolated from 7 genotypes were
characterized for eleven plant growth promoting activities and a trait index was
derived for each genotype showed that PUP 244 (1.49), Rasi (1.32) and Wauzhopek
(1.20) which were more P efficient had a higher index compared to other genotypes.
The rhizosphere SMBP was observed to be significantly higher in the genotype
PUP 244, Wauzhopek, Rasi and Swarna while in MTU 1010, ISM and PUP 236 had
significantly lower SMBP. Dehydrogenase activity was significantly high in the
rhizosphere soil of PUP 244 at all stages, followed by Rasi and Wauzhopek. The highest
activity of alkaline phosphatase and acid phosphatase were also observed in the
rhizosphere of PUP 244, Rasi, Wauzhopek and Swarna compared to MTU1010, ISM
and PUP 236.
Root length and root volume of PUP 244, Rasi and Wauzhopek were
significantly higher at all stages compared to MTU 1010 and ISM. At harvest, higher
depletion in total P was observed in the rhizosphere of PUP 244, Rasi and Wauzhopek
compared to other genotypes. Efficient genotypes had depleted the inorganic P and
organic P from the labile and moderately labile P forms indicating their ability to
effectively mineralize organic P in their rhizospheres. Total dry matter (TDM) and P
uptake by PUP 244 (TDM - 79.92 g, P uptake - 0.93 g TDM-1) was recorded high
which was followed by Rasi and Wauzhopek while ISM (TDM- 37.75 g; P uptake- 0.22
g TDM-1) and MTU 1010 (TDM- 32.80 g; P uptake- 0.23 g TDM-1) were observed to
be low.
To conclude, the study of different microbial and soil parameters in the
rhizosphere of low P efficient and non-efficient genotypes revealed that the efficient
genotypes such as Rasi, Wauzhopek, PUP 244 and Swarna supported higher microbial
populations with enriched PGP traits (including traits involved in phosphorus
solubilization and mineralization), higher SMBP which is considered a source of labile P
and increased dehydrogenase and alkaline and acid phosphatase enzyme activities in the
rhizosphere. These microbial differences have probably aided the efficient genotype in
retrieving P from non-labile pools and grow in the soil which contained low available P.
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D10,399