Biocontrol of charcoal-rot of sorghum by actinomycetes isolated from herbal vermicompost

Abstract

A total of 137 actinomycetes, isolated from 25 different herbal vermicomposts, were characterized for their antagonistic potential against Macrophomina phaseolina by dual-culture assay. Of them, eight most promising isolates (CAI-17, CAI-21, CAI-26, CAI-68, CAI-78, KAI-26, KAI-27 and MMA-32) were characterized for the production of siderophore, chitinase, protease, hydrocyanic acid (HCN), indole acetic acid (IAA) and further evaluated for their antagonistic potential against M. phaseolina by blotterpaper assay and in greenhouse. All the eight isolates produced HCN and IAA, seven produced siderophore (except CAI-78) and protease (except KAI-27) and four produced chitinase (CAI-26, KAI-26, KAI-27 and MMA-32). In the blotter-paper assay, no charcoal-rot infection was observed in KAI-26 and KAI-27-treated sorghum roots, indicating complete inhibition of the pathogen, while the other isolates showed 47 to 88% lesser charcoal-rot infection compared to the control. In the antifungal activity test against M. phaseolina (in greenhouse on sorghum), all the isolates increased in shoot dry mass by 28 to 53% and root dry mass by 5 to 21%, over the control. In order to confirm the plant growth promoting (PGP) traits of the isolates, the green house experiment was repeated, but in the absence of M. phaseolina. The results further confirmed the PGP traits of the isolates as evidenced by 15 to 34% increase in shoot dry mass on six isolates (except CAI-26 and KAI-27), 14 to 57% increase in root dry mass on five isolates (except CAI-68, KAI-26 and KAI-27), 17 to 60% increase in root length on five isolates (except CAI-17, CAI-21 and CAI-68) and 10 to 64% increase in root volume on six isolates (except CAI-17 and CAI-68). Culture filtrate of three potential actinomycetes (CAI-21, CAI-26 and MMA-32) at 0.5% inhibited the growth of M. phaseolina, indicating that the metabolites of these actinomycetes were responsible for the inhibition. The sequences of 16S rDNA gene of the isolates matched with Streptomyces but with different species in BLAST analysis. This study indicates that the selected actinomycetes have the potential for PGP and control of charcoal-rot disease in sorghum.

Evaluation ofStreptomycesspp. for their plant-growth-promotion traits in rice

“…Therefore it is concluded that the five Streptomyces strains used in this study were apparently well adapted not only in the sorghum rhizosphere (Gopalakrishnan et al 2011b) but also in the rice rhizosphere, in the present investigation, where they promoted plant growth. Further, the five Streptomyces strains could also be used as biocontrol agents against charcoal rot disease in sorghum.…”

“…Five Streptomyces strains reported in this study (CAI-17, CAI-68, CAI-78, KAI-26 and KAI-27) were known to be good biocontrol agents of sorghum charcoal rot disease as well as sorghum plant growth promoters by producing siderophore and indole acetic acid (IAA) (Gopalakrishnan et al 2011b). Siderophores produced by bacteria bind Fe 3+ from the environment and make it available to the plants in addition to its own growth (Wang et al 1993), whereas IAA-producing microorganisms are known to stimulate growth of the plants, particularly roots (Patten and Glick 2002); these two traits can be exploited by the host plants for their PGP.…”

“…The soil biological activities and mineral nutrients (including microbial biomass carbon and nitrogen, dehydrogenase, total N, available P and % organic carbon) in the Streptomyces-treated rice plots, at harvest, were also found significantly higher over the untreated control plots. The mechanism by which the Streptomyces strains enhanced morphological and yield traits of rice could be attributed to their enzymatic activities such as IAA and siderophore (direct stimulation of PGP) and/or chitinase, protease, hydrocyanic acid, cellulase, lipase and β-1,3-glucanase production capabilities (indirect stimulation of PGP; Gopalakrishnan et al 2011b). The influence of microorganisms on PGP including the root development of the plants has been reported by Birkhofer et al (2008), Uphoff et al (2009) and Gopalakrishnan et al (2011aGopalakrishnan et al ( , b, 2012a.…”

“…from rice straw compost; NCBI Accession number: JQ682624) and KAI-27 (Streptomyces spp. from rice straw compost; NCBI Accession number: JQ682625), reported earlier by us as potential for PGP and biocontrol traits in sorghum (Gopalakrishnan et al 2011b), were further studied.…”

“…Earlier, we reported a set of eight Streptomyces strains isolated from herbal vermicompost, with the potential for PGP and control of charcoalrot disease, caused by Macrophomina phaseolina (Tassi) Goid., in sorghum (Gopalakrishnan et al 2011b). The first three of the eight Streptomyces strains (CAI-21, CAI-26 and MMA-32) were also reported to have potential for PGP in rice (Gopalakrishnan et al 2012a).…”