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Volume 2, Issue 4      October-December, 2014

L-TRYPTOPHAN AMENDMENTS ENHANCED AUXIN PRODUCTION AND GROWTH OF TRITICUM AESTIVUM L. BY RHIZOBACTERIA
 
Anam Jamil and Basharat Ali*
Department of Microbiology and Molecular Genetics, University of the Punjab,
Quaid-e-Azam Campus, Lahore-54590, Pakistan
 
ABSTRACT
The objective of the present study was to evaluate the effect of co-inoculations of auxin producing Bacillus and Streptomyces strains to enhance the growth of Triticum aestivum L. For auxin production, Bacillus cereus McR-3, B. subtilis McR-7, Enterobacter cloacae FR, Streptomyces sp. RSF, S. macrosporeus SCF and S. griseoincarnatus CTF were screened by using colorimetric method. Auxin production was determined in the absence and presence of precursor i.e. L-tryptophan (0, 100, 300, 500 μg ml-I). Highest auxin production was recorded with B. subtilis McR-7 (31 μg ml-I), B. cereus McR-3 (28 μg ml-I) and E. cloacae (95 μg ml-I), respectively, in the presence of 100, 500, 500 μg ml-I L-tryptophan. After in vitro auxin screening, strains were evaluated for their growth stimulatory effects on T. aestivum under axenic conditions. In pot trials, strains showed variable growth responses when inoculated with single or mixed cultures. In single cultures, significant increase for root length (49%), shoot length (42%) and shoot fresh biomass (31%) was recorded respectively with Streptomyces sp. RSF and S. macrosporeus SCF. For mixed cultures, McR-3+SCF, FR+RSF and McR-7+SCF were the most promising to enhance shoot length (35%), root length (18%) and shoot fresh biomass (20%), respectively, over control. Overall, single and a few combinations of mixed cultures were most suitable to enhance growth of T. aestivum under axenic conditions. Results also indicated that consortia comprising of plant growth promoting rhizobacteria (PGPR) and Streptomyces offer good potential for the formulations of bio-inoculants for field trials.
Keywords: Bacterial auxin production, L-tryptophan, Rhizobacteria, Triticum aestivum, Plant growth promotion
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