One strain of Amycolatopsis sp. BCA-696, a rare genus of actinomycete, demonstrated previously for its plant growth-promotion traits in chickpea and sorghum, was tested for its antagonistic potential against Macrophomina phaseolina (the causal agent of charcoal rot disease of sorghum) by dual culture assay, metabolite production assay, and in greenhouse and field screens. In the dual culture and metabolite production assays, BCA-696 inhibited the growth of M. phaseolina. When BCA-696 was tested for its antagonistic activity under greenhouse and field conditions (two seasons) against charcoal rot of sorghum by tooth pick method of inoculation, it significantly reduced the disease. Scanning electron microscope analysis revealed that the xylem and phloem tissues of the BCA-696 treated stem samples were intact compared to that of disease control plants. This study indicates that the selected Amycolatopsis sp. BCA-696 has the potential to manage charcoal rot of sorghum.

Streptomycesalbus 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 Macrophomina phaseolina. Results exhibited that CAI-21 significantly inhibited the growth of the pathogen, M. phaseolina, 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 M. phaseolina 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 M. phaseolina 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 M. phaseolina in the poisoned food technique. This study indicates that S.albus CAI-21 and its active metabolite organophosphate have the potential to control charcoal rot in sorghum.

Main conclusion The findings of this study suggest that the selected five strains of Streptomyces spp. could be used for biological control of charcoal rot disease in sorghum.

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