Assessing the prospects of Streptomyces sp. RP1A-12 in managing groundnut stem rot disease caused by Sclerotium rolfsii Sacc

Abstract

Stem rot of groundnut caused by the soilborne pathogen Sclerotium rolfsii can cause significant yield losses. Biological control of stem rot using actinomycetes is a viable alternative to existing fungicidal management. Though actinomycetes are prolific antibiotic producers, reports pertaining to their use in groundnut disease management are limited. Here, actinomycetes were isolated from groundnut rhizospheric soils and screened for antagonism against S. rolfsii through a dual culture assay. Culture filtrates and crude extracts of the potential candidates were screened further for extracellular antifungal activity and characterized for biocontrol and plant-growth-promoting traits. A promising candidate was tested under greenhouse conditions as whole organism as well as crude extracts. Isolate RP1A-12 exhibited high antagonism against S. rolfsii in dual culture assay (69 % inhibition), culture filtrate assay (78-100 % inhibition at various concentrations) and crude extract assay (100 % inhibition with 1 % crude extracts). Moreover, germination of sclerotia of the test pathogen was inhibited with 1 % crude extracts. Strain RP1A-12 produced hydrogen cyanide, lipase, siderophores and indole acetic acid. Oxalic acid production by S. rolfsii was also inhibited by crude extracts of RP1A-12. In greenhouse studies, RP1A-12 reduced stem rot severity. Overall, our results suggest that isolate RP1A-12 has potential biocontrol capabilities against stem rot pathogen. Molecular characterization based on 16S rRNA gene sequencing of RP1A-12 identified it as a species of Streptomyces, closely related to S. flocculus.

Characterization of broad-spectrum biocontrol efficacy of Bacillus velezensis against Fusarium oxysporum in Triticum aestivum L.

“…In this study, none of the three tested isolates showed phosphate-solubilizing activity on NBRIP agar medium by establishing clear halo zones around the bacterial colony. Similar results were obtained by Jacob et al (2016), who showed promising findings from a GH (greenhouse) study, but the isolate was unable to demonstrate phosphate solubilizing activity.…”

“…This solution was incubated in the dark for 35 min. A change in colour from blue to orange showed a positive result for siderophore production (Jacob et al, 2016). Three replications were maintained, and uninoculated broth served as a control.…”

“…Approximately 1 mL of Nessler's reagent (0.09 molL −1 K2[HgI4] with 2.5 molL −1 KOH) was mixed with 9 mL of supernatant. The change in colour from brown to yellow showed the production of ammonia, and broth without Nesseler's reagent served as a control (Jacob et al, 2016).…”

Bioprospecting from plant waste composting: Actinobacteria against phytopathogens producing damping-off

“…Although the high temperatures generated during composting are considered an important factor of sanitation, it seems that the above mentioned biotic factors can significantly influence the elimination or deactivation of harmful agents, not only during the composting process, but also after the application of compost as a substrate to soils as well. With the specific case of actinobacteria, the ability to produce compounds with useful features in pharmacology, agriculture and biotechnology is widely known [20]. These products are currently expensive, so consider the ability of actinomycetes producing interesting substances as siderophores or chitinases to promote plant growth and enhance antagonism to phytopathogens, opens new and sustainable possibilities.…”

Assessing the potentials of bacterial antagonists for plant growth promotion, nutrient acquisition, and biological control of Southern blight disease in tomato

“…rolfsii , S . sclerotiorum , and Botrytis cinerea [ 53 , 54 ]. Therefore, oxalotrophic isolates of S .…”