Identification and Characterization of a Streptomyces albus Strain and Its Secondary Metabolite Organophosphate against Charcoal Rot of Sorghum.

Subramaniam Gopalakrishnan,Mahalingam Govindaraj,Rajan Sharma,Susana V Gonzalez,Sravani Ankati,Nimmala Naresh,Sambangi Pratyusha,Nebojsa Simic,Sondre Nervik,Suraj P Mishra,Vadlamudi Srinivas

doi:10.3390/plants9121727

Abstract

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.

Highlights

Sorghum [Sorghum bicolor (L.) Moench] is a nutrient-rich staple food crop for millions of rural communities in the semiarid tropics [1]
In the dual-culture assay, CAI-21 caused a 15 mm inhibition of M. phaseolina (Table 1 and Figure 1). This indicated the production of antifungal compounds that may be involved in the inhibition of the hyphal growth of M. phaseolina, as there was no direct contact between the M. phaseolina and CAI-21
Plant growth-promoting rhizobacteria (PGPR) strains are mainly regarded as biocontrol agents as they potentially produce siderophores, chitinase, and hydrocyanic acids (HCN), which induce disease resistance in agriculturally important crops [26,27]

Summary

Introduction

Sorghum [Sorghum bicolor (L.) Moench] is a nutrient-rich staple food crop for millions of rural communities in the semiarid tropics [1]. It is grown on 42 million hectares of land in the world, with a total production of 59 million tonnes [2]. Among the various biotic stresses of sorghum, charcoal rot, caused by Macrophomina phaseolina (Tassi) Goid., is an important disease of postrainy sorghum. It affects more than 500 plant species including legumes, vegetables, and cereals and devastates up to 100% of the crop [3].

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