Development of quality assurance method for biofertilizers using LACz marker
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Date
2004
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CCSHAU
Abstract
Biofertilizers are living microorganisms used to supplement nutritional
requirement of plants. Strains of Azotobacter, Rhizobium, Azospirillum, Pseudomonas, Bacillus
and Acetobacter have been developed as biofertilizers for various crops and are suppled as
carrier based inoculants. The responses of biofertilizers are inconsistent and generally related
to the poor quality and poor competitive ability of the inoculants. The quality control methods
include standard plate count and most probable number (MPN) by plant infection. Both these
methods are not very specific and require at least 10-30 days. Thus, the quality control methods
are not strictly followed because producers are not willing to hold their product for 30 days and
thus substandard biofertilizers are being supplied to the farmers. Thus, there is an urgent need
to develop simple method for quality assurance of biofertilizers, which could be completed with
in 6-12 hours.
lacZ marked strains of Azotobacter (A-2), Rhizobium (T-19CL and PP1021L),
Pseudomonas (P-35) and Bacillus (BPL-2) showed relationship between -galactosidase activity
with viable cell number at different stages of growth in liquid medium. The Z buffer with 0.1%
Triton X-100 was found to be the best diluent for enumeration of viable cell population in
charcoal based inoculants. There was relationship in -galactosidase activity and viable cell
number of all these above strains in charcoal based inoculants, which remained stable up to
three months. Time for development of yellow colour of ONPG filter paper discs was correlated
with viable cell number, thus providing the qualitative method for enumeration of viable cell
number in the bioinoculants.
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