~ 545 ~ Journal of Pharmacognosy and Phytochemistry 2019; SP2: 545-548 E-ISSN: 2278-4136 P-ISSN: 2349-8234 JPP 2019; SP2: 545-548 Mahalakshmi S Department of Agriculture Microbiology, Faculty of Agriculture, Annamalai University, Annamalai Nagar, Tamil Nadu, India M Vijayapriya Department of Agriculture Microbiology, Faculty of Agriculture, Annamalai University, Annamalai Nagar, Tamil Nadu, India N Pandeeswari Department of Agriculture Microbiology, Faculty of Agriculture, Annamalai University, Annamalai Nagar, Tamil Nadu, India Correspondence Mahalakshmi S Department of Agriculture Microbiology, Faculty of Agriculture, Annamalai University, Annamalai Nagar, Tamil Nadu, India Studies on developing PGPR consortium with improved shelf life Mahalakshmi S, M Vijayapriya and N Pandeeswari Abstract Plant growth promoting rhizobacteria (PGPR) are soil bacteria with some beneficial effects on soil properties. Plant growth promoting rhizobacteria are beneficial soil bacteria that colonize plant roots and enhance plant growth promotion activity by different mechanisms in various ways. The use of bio inoculants forms one of the vital components for a long-term sustainable agriculture system of any crop. Considering the potential of plant growth promoting rhizobacteria the knowledge on the association of PGPR will be of immense help for standardizing microbial inoculants to enhance the crop yield. In the present study an attempt has been made to develop a suitable consortium in a suitable formulation with improved shelf life to use as a prudential bio inoculants. An attempt was made to develop carrier based biofertilizer by using different isolates of PGPR viz., A. lipoferum TMAzs-13, P. fluorescents TMPs-19 + B. megaterium TMB-3 obtained in the present study with lignite, pressmud. The survivability was studied by monthly viable cell count of PGPR strains in single, dual inoculants, as well as in the consortium prepared with lignite and pressmud carrier materials upto six months of storage. The effect of different concentrations (1% and 2%) of Poly vinyl pyrollidone (PVP) on the survival of PGPR strains in lignite carrier was investigated. Keywords: PGPR, Carrier Materials, Poly vinyl pyrollidone Introduction PGPR have been applied to various crops that enhance the growth, seed emergence and crop yield and some have been commercialized (Dey et al., 2004; Herman et al., 2008; Minorsky 2008) [4] . PGPR organisms like Azospirillum, Azotobacter, Pseudomonas and Bacillus that have been shown to colonize the roots of various plants, and to increase the height, flower number, fruit number and total weight of tomato plants (Minorsky, 2008) [4] . A frequent observation is that in carrier based inoculants, the number of viable cells decreases from 10 9 to 10 7 colony forming units (CFU) per g after 90 days of storage (Okon et al., 1995). The most consistent feedback received from the farmers and inoculants producers is the concern about the the shelf life of carrier based inoculants, since they have shorter shelf life, which hardly ends beyond three to four month under normal storage conditions. The development of adequate formulations, which would ensure survival, protection of the strain and the application technology, which would allow timely, easy and precise delivery in the field could be a major step towards their goal. Hence techniques to increase the shelf life of inoculants thus become necessary to propagate their technology in large scale. The use of bio inoculants forms one of the vital components for a long-term sustainable agriculture system of any crop (Tilak et al., 2005) [12] . Considering the potential of Plant growth promoting rhizobacteria the knowledge on the association of PGPR will be of immense help for standardizing microbial inoculants to enhance the crop yield. In the present study an attempt has been made to develop a suitable consortium in a suitable formulation and studies to increase the shelf life of inoculants to use as a prudential bio inoculants for betterment of tomato. Efficient strains of nitrogen fixing and phosphate solubilizing microorganisms are mass multiplied under laboratory condition and mixed with a carrier. These carrier based inoculants are supplied to farmers for crop inoculation. Carrier is a medium or matrix on which inoculant microorganisms grow to a reasonably higher population for an initial period and thereafter decline. The nature of the carrier often determines the subsequent performance of the inoculant. The criteria for a good carrier material are no toxicity to the introduced microorganisms, good absorption capacity, suitable pH, and fine particle size for better adherence to seed, good water holding capacity and availability of materials at cheaper cost. Different carriers have been tested and used for inoculation throughout the world. Some of the carriers used by different manufactures in the country and abroad are peat, lignite, vermiculite,