Aspergilli and rhizobia are better co-inoculants as biofertilizers

Abstract

The application of synthetic phosphorous fertilizer is a routine agricultural practice. However, in nature in the soil, several phosphate-solubilising microbes (PSM) have been identified in the rhizosphere, and are of significance in organic farming. Two major PSM are Rhizobium sp. and Aspergillus sp. that has been identified to have the potential to establish as biofilms in the soil root-zone environment. As the fungi are capable of solubilising both organic and rock phosphates, co-inoculation of these two microbes will enhance the availability of available phosphates to plants and in turn will reduce the requirement of synthetic fertilizers. The present study aims to evaluate the survivability of these two organisms in vitro conditions as co-inoculants. Aspergillus sp. seemed to be more synergistic or associative in growth with the rhizobial strains, and this organism is known well as a rigorous PSM. The effect of rhizobial toxins on the isolated fungal strains and the fungal toxins on the isolated rhizobial strains were tested in this study. Results show that Aspergillus flavus 2 and Rhizobium sp. K 1 strains were found to be highly antagonistic and will be eliminated for further studies. Nevertheless, synergism was found to be highly variable amongst not only within rhizobial strains, but also amongst the isolated fungal strains.