Isolation and characterization of microbes for plant growth-promotion and biocontrol properties

Chickpea and sorghum are the two important crops grown in semi-arid tropics; several biotic factors were influencing the growth and yield of these crops. Chemical control is generally used to control the damage, but the indiscriminate use of chemicals lead to negative impacts on nature. Biological control is the safe and alternative method to control the pathogens as well as to promote plant growth, in which plant growth-promoting (PGP) microbes were used. In the present study, a total of 89 actinomycetes, 74 bacteria and 48 fungi were isolated from chickpea rhizosphere soil and vermicompost. The isolates were tested for their antagonistic potential against important fungal pathogens of chickpea and sorghum by dual culture, metabolite production assays. Based on the results of dual culture and metabolite production assays, four actinomycetes (viz. SAI-13, SAI-29, VAI-7 and VAI-40), four bacteria (viz. SBI-23, VBI-4, VBI-19 and VBI-23) and one fungal isolate (VFI-51) were selected for further studies. All the selected isolates possess plant growth-promotion (PGP) traits such as production of indole acetic acid (IAA), siderophore, protease, lipase, chitinase, cellulase and β,1-3 glucanase. All the selected isolate were able to tolerate harsh growth conditions such as high temperature (upto 40°C), pH (upto 11), salinity (upto 10 % NaCl) and resistant to fungicides such as Thiram, Bavistin, Benlate, Ridomil and Captan. The molecular identification studies revealed that all actinomycetes isolates belong to Streptomyces sp., all bacterial isolates belong to Bacillus sp. and the fungal isolate was identified as Penicillium citrinum. When the selected isolates were tested for their PGP ability under greenhouse (GH) and field conditions, all the isolates increased the growth and yield traits of chickpea and sorghum. The fungal isolate VFI-51 effectively controlled the pathogen M. phaseolina causing charcoal rot in sorghum under light chamber and GH conditions. All the selected isolates were able to colonize on root surface of chickpea and sorghum without causing damage to root surface. In qRT-PCR studies, there was an up-regulation of siderophore, IAA and β,1-3 glucanase genes. The active secondary metabolite from culture filtrates of Penicillium citrinum (VFI-51) was identified as ‘citrinin’ by NMR-MS studies and proved its efficacy in controlling the pathogen Botyrtis - 9 - cinerea under GH conditions. Hence, the selected isolates can be exploited for their PGP and biocontrol properties