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Keywords: Applied Sciences
Agriculture & related technologies
Soil Science
Issue Date: 2010
Abstract: The phosphorus content in soil (organic plus inorganic) is usually much higher than plant requirements, however bioavailability of phosphorus to plant is one of the major plant growth limiting constraints. Even the added P as phosphatic fertilizer may get unavailable because of its fixation/ precipitation in soil, particularly in calcareous and alkaline soils. Thus, there is dire need to mobilize this big pool of soil phosphorus for improving crop yields on sustainable basis and one of the strategies useful for this purpose is the use of specific microorganisms applied as inocula. Some plant growth promoting rhizobacteria (PGPR) are known to promote plant growth by solubilizing this unavailable/insoluble phosphorus (P) in soil while others enhance P acquisition by plant indirectly through promoting extensive root growth because of their 1- aminocyclopropane-1-carboxylate (ACC)-deaminase activity. As far as we know, for the first time we compared the PGPR carrying dual traits (phosphorus solubilizing and ACC deaminase activity) vs. single trait PGPR for their effectiveness to improve P nutrition and growth of wheat and maize. To achieve these objectives, a series of experiments was conducted to document the impact of selected PGPR on wheat and maize under axenic and natural conditions. A total of thirty five (35) isolates were collected from the rhizosphere of wheat and maize by using enrichment techniques. Six isolates were selected on the basis of their P-solubilizing and/or ACC deaminase activity. Among the selected six rhizobacteria, two (K1 & K2) predominantly carry ACC-deaminase activity, the other two (K3 & K4) had P-solubilization activity while rest of the two (K5 & K6) carried both of these traits. The seeds of wheat (Bhakar 2002) and maize (Sahiwal 2002) were inoculated with these six selected isolates and sown under axenic conditions in growth medium containing rock phosphate (RP) as P source. The same six strains of PGPR were tested under pot and field conditions with the objectives to improve P use efficiency in inoculated wheat and maize crop under five fertilizer treatment matrix including F0 (NK fertilizer only); F1, (F0+rock phosphate (RP); F2, (F0+DAP); F3, (F0+compost) and F4, (F0+RP-enriched compost). Inoculation with all the PGPR strains promoted growth and yield parameters of wheat and maize compared to respective uninoculated control under all the five fertilizer treatments, however, effectiveness of PGPR strains varied in different fertilizer treatments. Results also clearly revealed that dual trait PGPR strains were most promising and consistent in increasing growth and yield parameters of wheat and maize compared to single trait strains under all fertilizer treatments. Comparison of single trait PGPR indicated that P solubilizers were relatively more effective than those PGPR containing ACC deaminase activity implying that the improvement in P-nutrition is more critical for improving plant growth than just improving root growth with respect to P nutrition as well as growth and yield of wheat and maize. These results may imply that PGPR possessing dual traits could be the best candidates for formulation of the most effective and consistent biofertilizer. Overall, fertilizer treatments also differed from each other with respect to affecting growth and yield parameters of wheat and maize as fertilizer treatment F2, (F0+DAP) proved the best while F0, (N and K only) had the minimum impact.
Appears in Collections:PhD Thesis of All Public / Private Sector Universities / DAIs.

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