Harnessing the Untapped Cultural Diversity of Barnyard Millet Echinochloa Frumentacea Rhizosphere for Potential Biocontrol Agents with Plant Growth Promoting Attributes

Abstract

Phytopathogens, primarily fungi pose a significant threat to food production worldwide newlineand lead to increased dependency of agricultural community on fungicides and pesticides newlinedespite of their toxic impact on human health and environment. These problems call for ecofriendly newlinedisease management practices. Application of PGPR/biocontrol agents is the most newlinesuitable alternative in this context. Barnyard millet is grown for food and fodder in marginal newlineareas. This crop is stress tolerant, requires low input and under-researched in terms of its newlinerhizospheric microflora. In the present study, rhizospheric soil of barnyard millet was collected newlinefrom Chamoli, Pauri, Pithoragarh and Almora districts of Uttarakhand to explore potential newlinebacterial biocontrol agents which can inhibit two phytopathogens (Sclerotinia sp. and newlineA.alternata) of tomato and eggplant. Enumeration of microbial population from different soil newlinesamples revealed the presence of sufficient microbial load in the rhizosphere of the crop. newlinePresence of enzyme activities related to soil health also authenticated active microbial activity newlinein the test soils. Out of 176 bacterial isolates, recovered from barnyard rhizosphere, eighteen newlineisolates with best antagonistic activities against both the test fungi were tested for biocontrol newlinepotential using dual culture assay. Four bacterial isolates namely, AA17, AA12, MA13, and newlineMN8 showed maximum growth inhibition against both the fungal pathogens. Isolates were newlinecharacterized based on microbiological, biochemical and molecular properties including newlineamylase, siderophore, chitin hydrolysis, xyalanase, ammonia production, sugar utilization, newlinenitrate reduction etc. Maximum siderophore production and chitinase enzyme activity was newlinedetected in AA17 (89.7% and 0.072 and#956;mol min-1 respectively). Bacterial isolates AA17, AA12, newlineMA13 and MN8 were identified as Bacillus licheniformis, B.subtilis, Bacillus sp. and B.safensis newlineon the basis of 16S rDNA sequencing. A bacterial consortium (using 4 potential bacteria) was newlinedeveloped by testing their compatibility and its effect on mycelial weight inhibition along with newlineindividual bacterial isolates was analyzed. Consortium showed maximum weight reduction of newlinetest fungi (91.49% for A.alternata and 93.48% for Sclerotinia sp.) in comparison to individual newlineisolates. GC-MS analysis of ethyl extract of test bacteria revealed that a variety of organic newlinecompounds were present in the extracts of isolates and their consortium. Bis-ethyl-hexyl newlinephthalate was predominantly present in the extracts of all the bacterial isolates whereas, 2,4-ditert- newlinebutyl phenol showed maximum peak area (10.84%) in consortium extract. Both the newlineidentified compounds used in pure form inhibited fungal growth. Consortium and all the newlinebacterial isolates showed reduced percent disease incidence in plants challenged with newlineSclerotinia sp. where consortium showed maximum reduction (26.85%). Percent fruit rot was newlinereduced by 79.56% in tomato and 76.6 % in brinjal fruits. Significant effect was observed in newlineconsortium in comparison to individual bacteria in improving germination, agronomic and newlinebiochemical properties of tomato. An increase of 2.5 fold in chlorophyll content, 26.6% increase newlinein plant protein, and 1.8 fold increase in total sugar was observed in consortium treated plants newlineover untreated control. Thus barnyard millet can be a potential source of biocontrol agents with newlineplant growth promoting attributes. newline