Characterisation of plant growth

incubated at 30°C for 7 days. Appearance of red color in tubes indicated urea

hydrolysis (Lindstrom and Lehtomaki, 1988).

citrate utilization: Sodium citrate broth medium was modified by replacing the

carbon source with sodium citrate and bromothymol blue (25 mg/l). The tubes

containing modified media were stab-streaked with log phase culture of bacterial

isolates separately and incubated at 28±2°C for 24 h (Koser, 1923).

growth in presence of KNo ₃ : The ability of isolated strains to grow in presence

of 8% KNO ₃ was tested by inoculating the isolates separately on YEMA and NAM

plates containing 8% KNO _3. The plates were incubated for 28±2°C for 24 h (EI

Idrissi et al ., 1996).

Polyhydroxy Butyrate (PHB) accumulation: Bacterial isolates were inoculated

with respective media separately and incubated at 28±2°C and 150 rpm for 72 h.

After incubation, isolates were centrifuged at 10,000 rpm for 45 min to collect the

supernatant. Exopolysccharide (EPS) was precipitated by adding double volume

of chilled ethyl alcohol. The extracted EPS was dried at 45°C till constant weight

was achieved (Navarini et al., 1992).

Utilization of carbon sources: Utilization of various carbon sources by bacterial

isolates was done following El Idrissi et al., 1996. Himedia Carbohydrate™

Kit (Himedia Laboratories Pvt. Ltd., Mumbai, India) was used to determine

the 35 carbon source utilization that consisted of monosaccharides pentoses,

monosaccharides, hexoses, disaccharides, trisaccharides, polysaccharides, organic

compounds and sugar alcohol. Results of carbon utilization were analyzed by

using and MVSP (Multi Variant Software Package) version 3.21 software with

UPGMA clustering method.

Screening of plant growth promoting (PGP) endophytic bacterial isolates

The following PGP attributes of isolates were examined:

Phosphate Solubilization: Phosphate solubilization ability of isolates was

examined using Pikovaskya agar medium (Pikovskya, 1948). Isolates were spot

inoculated onto the Pikovaskya agar plates and incubated at 28±2°C for the 72h.

A clear zone formation around the spot was recorded. Solubilization index (S.I.)

was calculated as the ratio of halo zone diameter to colony diameter for positive

isolates (Vazquez et al ., 2000) following the formula:

SI=

Indole -3 acetic acid (Iaa) Production: To examine the IAA production by the

bacterial isolates, their log phase cultures were incubated on the broth medium

Int. J. Bioinformatics and Biological Sci.: v.2 n.1&2, p. 95-109. March & June 2014

99