Abstract
Introduction and exploitation of plant growth promoting rhizobacteria (PGPR) in agro-ecosystems enhance plant–microbes interactions that may affect ecosystems sustainability, agricultural productivity, and environmental quality. The present study was conducted to isolate and identify PGPRs associated with maize (Zea mays L.) from twenty sites of Himalayan region of Hajira-Rawalakot, Azad Jammu and Kashmir (AJK), Pakistan. A total of 100 isolates were isolated from these sites, out of which eight (HJR1, HJR2, HJR3, HJR4, HJR5, MR6, HJR7, HJR8) were selected in vitro for their plant growth promoting ability (PGPA) including phosphorus solubilization, indole-3-acetic acid (IAA) production and N2 fixation. The 16S rRNA gene sequencing technique was used for molecular identity and authentication. Isolates were then further tested for their effects on growth and nutrient contents of maize (Z. mays L.) under pouch and pot conditions. The 16S rRNA gene sequencing and phylogenetic analysis identified these isolates belong to Pseudomonas and Bacillus genera. The isolates promoted plant growth by solubilizing soil P which ranged between 19.2 and 35.6 μg mL-1. The isolates HJR1, HJR2, HJR3, and HJR5 showed positive activity in acetylene reduction assay showing their N2-fixation potential. All eight isolates showed the potential to produce IAA in the range of 0.9–5.39 μg mL-1 and promote plant growth. Results from a subsequent pot experiment indicated PGPRs distinctly increased maize shoot and root length, shoot and root dry weight, root surface area, leaf surface area, shoot and root N and P contents. Among the eight isolates, HR3 showed a marked P-solubilizing activity, plant growth-promoting attributes, and the potential to be developed as a biofertilizers for integrated nutrient management strategies.
Highlights
Intensive farming practices that achieve high yield require continuous application of chemical fertilizers in our agroecosystems
Isolation and Characterization of plant growth promoting rhizobacteria (PGPR) Among the 100 bacterial isolates from the twenty maize growing sites, eight named as HJR1, HJR2, HJR3, HJR4, HJR5, MR6, HJR7, and HJR8 were selected based on their ability to produce phytohormone indole-3-acetic acid (IAA), solubilize insoluble phosphate, or fix N2
The results indicated that the growth traits recorded under HJR3+1/2NP treatment were significantly (P ≤ 0.05) higher than those recorded under other isolates, TABLE 4 | Effect of inoculation with plant growth promoting rhizobacteria on the growth of maize (Zea mays L.) grown in pots under greenhouse conditions
Summary
Intensive farming practices that achieve high yield require continuous application of chemical fertilizers in our agroecosystems. The prices and availability of these chemical fertilizers become the limiting factor for crop production especially in developing countries around the world. It has been reported that more than 80% of applied P as fertilizers precipitates in the presence of metal ion complexes in soil (Ca2+ in calcareous soils and Fe3+ and Al3+ in acidic soils; Qureshi et al, 2012). In addition to these constraints, the prices of P fertilizers jumped up several folds during recent years making P fertilizers not-affordable to a common resource poor farmer
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