Role of microflora on the quality of vermi-products in improving plant growth

Abstract

A study on ‘Role of microflora on the quality of vermi-products in improving plant growth’ was carried out in the department of Plant Pathology, College of Horticulture, Vellanikkara during 2005-07.

The native microflora associated with the earth worm Eisenia foetida and different vermi-products viz., vermicompost, vermicasting and two types of vermiwash were isolated. Quantitative estimation of microflora revealed that, bacterial population was predominant in vermi-products followed by actinomycetes and fungi. Altogether, 32 fungi, 39 bacteria (including five nitrogen fixing and three phosphorus solubilizing bacteria) and four actinomycete isolates were selected for further work. These isolates were then tested for their efficiency in nitrogen fixation, phosphorus solubilization and antagonistic properties against Rhizoctonia solani, the leaf blight pathogen in amaranth. Based on the efficiency of the above aspects, one isolate each of nitrogen fixing and phosphorus solubilizing bacteria were selected. These isolates were tentatively identified as Azotobacter sp. (NB2) and Pseudomonas sp. (PB1) respectively. Seven isolates of fungi which recorded the promising antagonistic index (AI) and two isolates of bacteria which recorded highest per cent inhibition against R. solani were selected. The fungal isolates were identified as T. harzianum (VF5, VF22 and VF25), T. viride (VF8 and VF16), A. niger (VF2) and A. flavus (VF15). The bacterial isolates were tentatively identified as Bacillus sp. (VB4) and non fluorescent Pseudomonas (VB26). Then three different microbial consortia were prepared using the selected fungal and bacterial isolates alone and in combination.

A pot culture experiment was conducted to evaluate the efficacy of these consortia in improving plant growth in comparison to vermi-products. It was found that consortia including both fungal and bacterial isolates found to improve the plant growth by increasing yield other biometric characters. Observations on incidence and severity of leaf blight in amaranth showed that microbial consortia and non sterilized vermi-products had a favorable effect in checking the disease incidence. Considerable variation in population of soil microflora was observed among different treatments. Uptake of major nutrients was found to be more in treatments appied with vermicompost and vermicasting.

The in vitro studies on the effect of vermi-products on beneficial and pathogenic microorganisms revealed that steam sterilized extracts inhibited the growth of Rhizoctonia sp. and Colletotrichum sp. and did not inhibit the growth of Trichoderma harzianum and Pseudomonas fluorescens. Vermi-products lost its inhibitory activity after strong heating. Autoclaved extracts of vermi-products did not show inhibition on any of the four organisms tested.