| Summary: | <i>Streptomyces</i><i>albus</i> strain CAI-21 has been previously reported to have plant growth-promotion abilities in chickpea, pigeonpea, rice, and sorghum. The strain CAI-21 and its secondary metabolite were evaluated for their biocontrol potential against charcoal rot disease in sorghum caused by <i>Macrophomina phaseolina</i>. Results exhibited that CAI-21 significantly inhibited the growth of the pathogen, <i>M. phaseolina</i>, in dual-culture (15 mm; zone of inhibition), metabolite production (74% inhibition), and blotter paper (90% inhibition) assays. When CAI-21 was tested for its biocontrol potential under greenhouse and field conditions following inoculation of <i>M. phaseolina</i> by toothpick method, it significantly reduced the number of internodes infected (75% and 45% less, respectively) and length of infection (75% and 51% less, respectively) over the positive control (only <i>M. phaseolina</i> inoculated) plants. Under greenhouse conditions, scanning electron microscopic analysis showed that the phloem and xylem tissues of the CAI-21-treated shoot samples were intact compared to those of the diseased stem samples. The culture filtrate of the CAI-21 was purified by various chromatographic techniques, and the active compound was identified as “organophosphate” by NMR and MS. The efficacy of organophosphate was found to inhibit the growth of <i>M. phaseolina</i> in the poisoned food technique. This study indicates that <i>S.</i><i>albus</i> CAI-21 and its active metabolite organophosphate have the potential to control charcoal rot in sorghum.
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