The main objective of the present study was to isolate and characterize actinomycetes for their plant growth-promotion in chickpea. A total of 89 actinomycetes were screened for their antagonism against fungal pathogens of chickpea by dual culture and metabolite production assays. Four most promising actinomycetes were evaluated for their physiological and plant growth-promotion properties under in vitro and in vivo conditions. All the isolates exhibited good growth at temperatures from 20 °C to 40 °C, pH range of 7–11 and NaCl concentrations up to 8%. These were also found highly tolerant to Bavistin, slightly tolerant to Thiram and Captan (except VAI-7 and VAI-40) but susceptible to Benlate and Ridomil at field application levels and were found to produce siderophore, cellulase, lipase, protease, chitinase (except VAI-40), hydrocyanic acid (except VAI-7 and VAI-40), indole acetic acid and β-1,3-glucanase. When the four actinomycetes were evaluated for their plant growth-promotion properties under field conditions on chickpea, all exhibited increase in nodule number, shoot weight and yield. The actinomycetes treated plots enhanced total N, available P and organic C over the un-inoculated control. The scanning electron microscope studies exhibited extensive colonization by actinomycetes on the root surface of chickpea. The expression profiles for indole acetic acid, siderophore and β-1,3-glucanase genes exhibited up-regulation for all three traits and in all four isolates. The actinomycetes were identified as Streptomyces but different species in the 16S rDNA analysis. It was concluded that the selected actinomycetes have good plant growth-promotion and biocontrol potentials on chickpea.

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A study was carried out to test the effect of direct and indirect plant growth-promoting traits of bacteria, isolated from compost and rhizosphere soils, on chickpea. A total of 74 bacteria were isolated from herbal vermicomposts and rhizosphere soils of chickpea and screened for their antagonistic potential against soil-borne fungal pathogens of chickpea. Of which, four bacterial isolates (VBI-4, VBI-19, VBI-23, and SBI-23) were found to be promising in both dual culture and metabolite production assays. These isolates were identified as Bacillus species by 16S ribosomal DNA (rDNA) sequence analysis. Under in vitro conditions, all the isolates were found to produce protease, cellulase, β-1,3-glucanase, siderophore, indole acetic acid, lipase (except VBI-19), and hydrocyanic acid (except VBI-23 and SBI-23). All the isolates were tolerant to fungicides such as bavistin, captan, benlate, ridomil (only VBI-23 and SBI-23), and thiram (only VBI-4 and VBI-19) at field application rates. The isolates were also found to tolerate NaCl concentration of up to 8 % (VBI-23 up to 10 %), temperature range of 20 to 40°C, and a pH range of 7 to 11 (SBI-23 up to only 9). When the isolates were evaluated for their plant growth promotion (PGP) ability under greenhouse and field conditions on chickpea, all the isolates were able to increase growth parameters including nodule number, plant growth, and yield parameters when compared to uninoculated control. The isolates also increased the soil mineral properties including total N, available P, organic carbon (OC) %, microbial biomass C, and dehydrogenase activity in rhizosphere, at both flowering and harvest stages over the uninoculated control plots. All the isolates were found to colonize chickpea roots when observed under scanning electron microscope. This investigation indicated the PGP potential of selected bacteria in chickpea cultivation.

In our earlier investigation, a fungal isolate Penicillium citrinum VFI-51 and its secondary metabolite was reported to have antagonistic potential against Botrytis cinerea, the causative agent of Botrytis gray mold disease in chickpea. In the present investigation, P. citrinum VFI-51 was further evaluated for its antagonistic potential against Macrophomina phaseolina, the causative agent of charcoal rot in sorghum. P. citrinum VFI-51 inhibited M. phaseolina in both dual culture as well as secondary metabolite production assays. In the in vivo blotter paper assay, under light chamber conditions, P. citrinum VFI-51 controlled 85% of the charcoal rot disease on the roots when compared to the positive control. Under greenhouse conditions, when M. phaseolina was inoculated by tooth pick method in to the stalk of sorghum plant, the charcoal rot disease was controlled by 75% in P. citrinum VFI-51 treatment over the positive control. This study demonstrates the biocontrol potential of P. citrinum VFI-51 against charcoal rot of sorghum.