Isolation and characterization of pesticide resistant strains of Azotobacter spp., Azospirullum spp., Rhizobium spp. and phosphate solubilizing microorganisms and their application as biofertilizers

The purpose of the study was to screen for pesticide resistant isolates of plant growth promoting microorganisms such as Azotobacter spp., Azospirullum spp., Rhizobium spp. and phosphate solubilizers, the activity of which would not be affected by the presence of pesticides owing to their pesticide resistance; and to check their efficacy as biofertilizers. Screening was carried out using rhizospheric soil samples from fields treated with pesticides. The isolates were checked for resistance to six commonly used pesticides. The pesticide resistant isolates obtained were further shortlisted on the basis of high phytostimulation ability, and high solubilization index in case of phosphate solubilizers. These isolates also proved to be effective against a variety of bacterial and fungal phytopathogens. It was seen that the pesticide resistance of phosphate solubilizer isolate Enterobacter aerogenes strain HK 20-1 (as identified by biochemical as well as 16S rRNA identification) can be attributed to two proteins of molecular weight approximately 100 and 110 KDa. Plant studies and viability studies proved that the isolates, mainly the consortium not only proved to be effective in promoting growth of tomato plant in presence of 1000 ppm of six commonly used pesticides, but also proliferated in pesticide contaminated soils and improved the soil quality. These studies indicate that the isolates can be used as potential biofertilizers in pesticide contaminated fields, thus bringing about enhanced plant growth even in the presence of pesticides.