Thirty-one cultures of bacteria (W1, W2, ... W31) were isolated from the rhizosphere of different varieties of wheat and twenty-eight (R1, R2 ... R28) from the rhizosphere of rice growing at different sites. They were tested in the liquid medium and in soil to evaluate their relative efficacy for auxin biosynthesis by colorimetry. Among different rhizobacterial isolates, W9 showed significantly higher auxin production in liquid culture both in the presence and absence of its precursor, L-tryptophan (L-TRP). Four isolates showing maximum auxin production from each crop were selected. They were further tested for their ability to produce L-TRP (6.0 g kg-1 soil)-derived auxins both in non-sterilized and sterilized soils at 7.0 pH, 35oC temperature and 48 hours incubation period under static and shaking (150 rev. min-1) conditions. L-Tryptophan-derived auxin biosynthesis was also measured by supplementing with glucose (6.0 g kg-1 soil) under similar conditions. Results revealed that isolates W11 and W9 showed maximum auxin production at 6.0 g L-TRP kg-1 soil which was 66.3 and 27.5 μg g-1 soil in non-sterilized and sterilized soils, respectively, under static conditions. However, auxin synthesis at shaking condition was doubled to that produced under static environment. Rice isolates R20 and R27 were most active in producing auxins when soils were supplemented with glucose along with L-TRP. Glucose application had also positive effect on L-TRP-derived auxins over L-TRP alone.
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Azeem Khalid, Muhammad Arshad, Zahir Ahmad Zahir and Muhammad Khalid, 2001. Relative Efficiency of Rhizobacteria for Auxin Biosynthesis . Journal of Biological Sciences, 1: 750-754.
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