Isolation and characterization of secondary metabolites of actinomycetes against plant pathogens of chickpea and sorghum

Actinomycetes are known to have plant growth promoting traits and antagonistic activity against plant pathogens. The objective of the present experiment is to isolate the promising strains of actinomycetes against pathogenic fungi and to isolate the metabolites responsible for it. The fungal pathogens studied include Sclerotium rolfsii, Rhizoctonia bataticola (three strains viz. RB-6, -24 and -115) Fusarium oxysporum f. sp. ciceri, Botrytis cinerea, and Macrophomina phaseolina causes collar rot, dry root rot, Fusarium wilt, Botrytis grey mould diseases in chick pea and charcoal rot in sorghum, respectively

Plant growth-promotion by Streptomyces spp. in sorghum (Sorghum bicolor L.)

Seven strains of Streptomyces spp.: BCA-546 (KF770898), BCA-659 (KF770889), BCA-667 (KF770888), BCA-689 (KF770899), BCA-698 (KF770900), CAI-133 (KF770895) and CAI-8 (KF770890), reported earlier to produce biocontrol and plant growth-promoting (PGP) substances were further evaluated for PGP traits in sorghum under greenhouse and field conditions. Under greenhouse conditions, plant height, leaf area and weight, root length and weight, shoot weight, panicle weight and seed weight were enhanced in plots inoculated with Streptomyces spp. than the un-inoculated control at 30, 60 days after sowing (DAS) and at final harvest. Similarly, treatment with Streptomyces spp. led to growth and yield enhancements under field conditions at 60 DAS and final harvest. Among the seven strains, BCA-698, BCA-689, BCA-546 and BCA-659 were found to be superior for PGP. Under field conditions, at both flowering and harvest stages, the soil organic C, available P and total N were also found to improve with Streptomyces spp. treatments. A scanning electron microscopic study showed extensive root colonization of sorghum. The gene expression profiles revealed up-regulation of β-1,3-glucanase, indole acetic acid (IAA) and siderophore genes. Based on the present findings, the seven selected Streptomyces strains could be employed to enhance plant growth and yield in sorghum.Keywords: Gene expression, plant growth-promotion, scanning electron microscopy, sorghum, Streptomyces spp

Efficacy of Jatropha, Annona and Parthenium biowash on Sclerotium rolfsii, Fusarium oxysporum f. sp. ciceri and Macrophomina phaseolina, pathogens of chickpea and sorghum

The demand for products and technologies based on plants to control plant pathogens has increased in recent years due to concern about the use of hazardous pesticides. In the present investigation, washings of vermicompost (called biowash) prepared from foliage of Jatropha (Jatropha curcas), Annona (Annona squamosa) and Parthenium (Parthenium  hysterophorus) were evaluated against fungal pathogens viz. Fusarium oxysporum f. sp. ciceri (FOC; causes wilt in chickpea), Sclerotium rolfsii (causes collar rot in chickpea) and Macrophomina phaseolina (causes charcoal rot in sorghum). Crude biowash of the botanicals were partitioned against ethyl acetate and the resultant organic and aqueous fractions were tested against the fungi. Similarly, crude biowash was also passed through C18 solid phase extraction cartridges and the resultant adsorbed and non-adsorbed fractions were tested against the fungi. Organic fractions of all the three biowash at 0.5% inhibited the growth of S. rolfsii between 78 and 87%, M. phaseolina between 62 and 65%, whereas only Parthenium was able to effectively inhibit FOC (91%), compared to control. Adsorbed fractions of all the three biowash at 0.5% inhibited the growth of S. rolfsii between 81 and 92%, M. phaseolina between 76 and 77% and FOC between 26 and 49%, compared to control. Both aqueous and non-adsorbed fractions of all the three biowash did not inhibit any of the fungi. Since Jatropha biowash showed consistently higher levels of inhibition (>80%) in both fractionation methods on S. rolfsii, this was selected for further purification of their secondary metabolites. When the organic fraction of Jatropha  biowash was further fractionated by C18 open column chromatography with eluent 5, 10, 20, 40, 60, 80 and 100% MeOH fractions, only 80% methanol (MeOH) fraction was found to inhibit S. rolfsii. The active 80% MeOH fraction showed three clear bands when chromatographed on Silica Gel 60 F254 thin layer chromatography (TLC) plates with Rf values 0.95, 0.90 and 0.70. Hence, it was concluded that one of these three bands could be the activeingredients that inhibited S. rolfsii and can be further exploited as a bio-fungicide.Key words: Botanicals, jatropha, annona, parthenium, biowash, Sclerotium rolfsii, Fusarium oxysporum f. sp. ciceri, Macrophomina phaseolina, secondary metabolites