Abstract
The screening of plant growth promoting rhizobacteria is a crucial step for their utilization as beneficial input in improving the crop productivity. This study was carried out to screen and evaluate the auxin producing rhizospheric isolated Pseudomonas strains for their potential to improve growth of Triticum aestivum (wheat) plant under laboratory and natural conditions. Three strains PNS-4, PNS-6 and PNS-15 were evaluated for auxin production by Salkowski’s method and further confirmed by high performance liquid chromatography (HPLC). The PNS-4, PNS-6 and PNS-15 strains were identified by I6S rRNA gene sequencing that showed maximum resemblance with Pseudomonas mendocina (99%), Pseudomonas alcaliphila (99%) and Pseudomonas sp. (99%) respectively. Selected strains were found to produce auxin with and without the amendment of exogenously applied L-tryptophan, a major precursor for auxin biosynthesis and an important constituent of plant root exudates. Efficacy of these strains on wheat plant growth was checked under laboratory and field conditions. All Pseudomonas species were found to improve the % seed germination and growth parameters (shoot length, root length, fresh weight and dry weight) of the wheat seedlings significantly (P = 0.05) as compared to the un-inoculated seedlings under laboratory condition. The biochemical parameters (total soluble protein content and endogenous auxin content) of the bacterial inoculated wheat seedling were also increased significantly than that of uninoculated ones. Under natural condition, seed bacterization also showed the significant effect (P = 0.05) on yield parameters (shoot length, number of tillers, spike length and weight of seeds in grams) of the wheat plants when compared with non-inoculated plants. Our results reported the three most promising Pseudomonas candidates and revealed the fact that experiments under laboratory and natural conditions may be helpful in selecting the best candidates as bio fertilizers for future agricultural practices.
Highlights
Complex diversity of microbes interacts with plant roots continuously in rhizospheric soil region
The nucleotide sequences have been submitted in GENBANK under accession number of JF 905443.1, JF905444.1 and JQ218449 for PNS-4, PNS-6 and PNS-15 respectively (Table 1)
In vitro auxin production and screening of rhizobacterial isolates for plant growth promotion under gontobiotic conditions are considered as useful approach for selecting PGPR [28]
Summary
Complex diversity of microbes interacts with plant roots continuously in rhizospheric soil region. These microbes can influence the plant growth in various ways that can be beneficial or detrimental to the plant development [1,2]. Beneficial rhizospheric microorganisms gained special attention due to their potential to enhance the plant growth by variety of mechanisms. Some mechanisms are involved in plant growth promotion directly i.e. phytohormone [3] and siderophore production [4], phosphate solublization [5], nitrogen fixation and denitrification [6,7] and 1-amino-cyclopropane-1-carboxylate deaminase production [8]. Phytohormone production has been studied as one of the main mechanisms by which PGPR may enhance the plant growth [11]. Several genera of Pseudomonas, Bacillus, Arthrobacter, Azospirillum, Klebsiella, and Enterobacter, isolated from rhizospheric region of variety of crops, have been evaluated for plant growth promoting attributes and illustrated their synergistic effects on plant growth and development [12,13]
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