Evaluation of Biochar as a Carrier Material of Antagonistic Rhizobacteria for the Management of Root Pathogenic Fungi of Chickpea

Abstract

Root diseases either soil or seed borne poses serious implications on seed germination and subsequently plant growth and development. The attack of root diseases in earlier stages of the crop completely destroys the crop resulting in unrecoverable losses. Biological control offers great potential to resist the pathogenic microbes to develop in rhizosphere subsequently reducing the attack. However persistency and sustainable number of biological control agent must be there to fight against the pathogens. In this study we determined the biochar as a carrier of antagonistic rhizobacteria and how much effective biochar is in sustaining the bacterial count in the rhizosphere and also during storage. We further determined the effect of biochar on root nodulating factors that are being altered by biochar alone and also with bacterial inoculant. This study was initiated with survey to determine the prevalence, incidence and severity of major fungal root pathogens infecting chickpea crop in major chickpea growing areas of Punjab i.e. districts Layyah and Bhakkar. Surveys were conducted during year 2013-14 and 2014-15 in the months of November to March. From each district twenty areas and three fields from each area were visited making total 120 fields. Results revealed 100% prevalence of root diseases in every single field and average highest incidence in Layyah was 60.05% and in Bhakkar it was 57.5%. The minimum and maximum incidence in Layyah and Bhakkar was 52%-72%, 48%-76% and 48%-76%, 50%-70% during 2013-14 and 2014-15 respectively. Disease severity ranged from 1-4 in almost every area/field visited. Collected samples retrieved five fungal pathogens and the most frequent was F. oxysporum f. sp. ciceri, with average highest frequency of 88.5% followed by M. phaseolina and Verticillium spp. with 46.5% and 24.5% respectively. Results xxii elucidated that fungal pathogens associated to roots of chickpea pose serious implications on growth and productivity of chickpea. The rhizobacteria i.e. Paenibacillus illinoisensis Rh-31 and Mesorhizobium ciceri antagonistic to fungal pathogens were inoculated to several biochar (Wheat straw (WS), Sheesham wood (SW), Sugarcane bagasse (SB) and Acacia wood (AW)) and their concentration was investigated at regular intervals of 30 days till 180 days. Highest bacterial count (cfu/g) was obtained with SB biochar even after 180 days. It was noticed that biochar held much more bacterial cells as compared to peat and pH of the carrier material seemed to be the key factor in determining the ability of compound to serve as carrier. The impact of carrier materials on disease and plant growth was studied under greenhouse conditions. SB Biochar with rhizobacteria showed significant results in decreasing the disease incidence and increasing plant growth. The effect of biochar on nodulating genes was studied by qPCR and it was noticed that expression of all genes was upregulated in real time PCR and synergistic treatments (Mesorhizobium ciceri + SB biochar) plants showed noteworthy difference from non-inoculated and independently treated with rhizobia and biochar plants. Further testing of biochar under field conditions also showed better growth as compared to non-treated plants. Therefore on the basis of results it is concluded that sugarcane bagasse biochar can be used as a good carrier material of bacterial inoculant for long term storage and also for application in the field.