Streptomyces strain KX852460 having antifungal activity against Rhizoctonia solani AG-3 KX852461 that is the causal agent of target spot disease in tobacco leaf. The aim of the study was to determine the antifungal activity of Streptomyces strain KX852460 extract against R. solani AG-3 and to identify bioactive antifungal compounds produced by strain KX852460. Crude substance was produced by submerged fermentation process from Streptomyces strain KX852460. Various solvent was used to extract the culture filtrate. Among all, ethyl acetate extracted supernatant showed great potency against R. solani AG-3 KX852461. The active fractions were purified by silica gel column chromatography having 52 mm zone of inhibition against R. solani AG-3 KX852461. The purified fractions were identified by gas chromatography–mass spectrometry technique. Twenty-seven compounds were identified and most of the compounds were the derivatives of aromatic compounds. Eicosane (C20H42) and dibutyl phthalate (C16H22O4) were found antifungal compounds in this study. While morphinan, 7,8-didehydro-4,5-epoxy-17-methyl-3,6-bis[(trimethylsilyl)oxy]-, (5.Alpha. 6.Alpha)—(C23H35NO3Si2), cyclononasiloxane, octadecamethyl—(C18H54O9Si9) and benzoic acid, 2,5-bis(trimethylsiloxy) (C16H30O4Si3) were the major compounds with highest peak number. These results suggested that Streptomyces strain KX852460 had good general antifungal activity and might have potential biocontrol antagonist against R. solani AG-3 KX852461 to cure the target spot in tobacco leaf.

A novel Bacillus amyloliquefaciens BAM strain, with novel fermentation nutrient mediums and compositions, could produce potent antifungal secondary metabolites, as the existing strains face resistance from fungus pathogens. In the current study, we introduced two novel nutrient mediums for the fermentation process, semolina and peanut root extract, as carbon and nitrogen sources in order to maximize the antifungal effects of B. amyloliquefaciens against Cercaspora arachidichola to control early leaf spot disease in peanuts. Based on a single-factor test and the central composite design of response surface methodology, the optimum fermentation medium for Bacillus amyloliquefaciens antagonistic substance was determined, containing 15 gm/L of semolina flour, 12.5 gm/L of beef extract, and 0.5 gm/L of magnesium sulfate, which inhibited the fungal growth by 91%. In vitro, antagonistic activity showed that the fermentation broth of B. amyloliquefaciens BAM with the optimized medium formulation had an inhibition rate of (92.62 ± 2.07)% on the growth of C. arachidichola. Disease control effects in pot experiments show that the pre-infection spray of B. amyloliquefaciens BAM broth had significant efficiency of (92.00 ± 3.79)% in comparison to post-infection spray. B. amyloliquefaciens BAM broth significantly promoted peanut plant growth and physiological parameters and reduced the biotic stress of C. archidechola. Studies revealed that B. amyloliquefaciens BAM with a novel fermentation formulation could be an ideal biocontrol and biofertilizer agent and help in early disease management of early leaf spots in peanuts.

In this study a strain of Streptomyces sp. was isolated from soil and identified by 16S rRNA gene sequencing technology. The strain was screened for antibiotics production effective against biocontrol of Rhizoctonia solani AG-3 to cure the target spot disease in tobacco. For enhance production of secondary metabolites, central composite design of response surface methodology (RSM) was applied in submerged fermentation. The maximum metabolite production was using medium volume of 55 mL in 250 mL flask, agitation speed of 165 rpm, incubation temperature 30 °C, initial medium pH of 6.8 and inoculum size of 7%. Solvent extraction method was used to extract the secondary metabolites and active compounds were purified by silica gel column chromatography. The purified fractions were further investigated by gas chromatography-mass spectrophotometer (GC-MS). GC-MS analysis showed 48 compounds, among them 12 were active against pathogen. These findings indicated that the strain Streptomyces TA 1123 was a potential antagonist against R. solani AG-3.

A bioactive strain Streptomyces diastatochromogenes KX852460 was selected for the production of secondary metabolites to control the target spot disease on tobacco leaves, caused by the Rhizoctonia solani AG-3. Peanut meal, soluble starch, NaCl, yeast extract, and ammonium sulphate were identified the best ingredient for high antifungal activity of S. diastatochromogenes KX852460 against the R. solani AG-3. For the improved production of secondary metabolites, central composite design of response surface methodology was applied in submerged fermentation. The best concentrations of ingredients were peanut meal 4.88%, soluble starch 4.40%, NaCl 0.52%, yeast extract 0.47%, and ammonium sulphate 0.0360%. Study of metabolism changes in the submerged fermentation process was analyzed. Level of the reducing sugar increased, as the total sugar consumed. Amino nitrogen and total sugar decrease tendency, which indicated the growth of bacteria in submerged fermentation batch. Production of secondary and other metabolites influenced the pH of the fermentation batch.

A microbe-based silver nanoparticle could inhibit the tobacco mosaic virus. In the present study, AgNO₃ reacts with Pseudomonas fluorescens CZ strain fermentative broth and formed silver nanoparticles. The crystallinity and purity of silver nanoparticles (AgNPs) were examined by an X-ray diffractometer. Number of Bragg reflection was indexed in the face-centered AgNPs to show a cubic structure. Observation of scan electron microscope (SEM) confirmed the formation of AgNPs. Antiviral effects determined by percentage inhibition of local lesion of tobacco mosaic virus (TMV). Spray of AgNPs and inoculation with TMV assayed analysis revealed percentage inhibition of local lesion 92.70. Effects of AgNPs on the morphology of TMV were observed by a transmission electron microscope (TEM). Micrograph images confirmed the significant effects on the morphology of TMV. Biogenic NP from AgNO₃ and fermented broth from Pseudomonas fluorescens could be a potent approach to control the TMV.

In the submerged fermentation process, the introduction of novel nutrient media as sources of carbon and nitrogen can enhance antifungal activity. In this study, we used a submerged fermentation process to find the optimal media for the Bacillus velezensis BP-1 strain to grow in, and that would boost its antifungal activity against Peyronellaea arachidicola. By using a single-factor test and central composite design (CCD) in the response surface methodology, the optimal fermentation medium for the B. velezensis BP-1 strain was identified. The antagonistic potential of B. velezensis BP-1 was assayed against the P. arachidicola fungus to manage web blotch disease in peanut plant leaves. The LB medium was screened as the best medium, with a maximum antifungal activity of 90% in comparison to the other mediums. Semolina flour as the carbon source, peanut root extract as the nitrogen source, and magnesium sulfate as the inorganic salt were selected as the best nutrient components in comparison to the others. The response surface methodology was optimized by using 15 g/L of semolina flour as the carbon source, 13.68 g/L of peanut root extract as the nitrogen source, and 0.50 g/L of magnesium sulfate as the inorganic salt, achieving 90% inhibition of P. arachidicola. The in vitro bioassays showed that the optimized fermentation broth of B. velezensis BP-1 had significant antifungal activity, with an inhibition rate of 88.34% against P. arachidicola. In the pot experiments on disease control, the management effects revealed that the pre-inoculation spray of the B. velezensis BP-1 broth had significant efficiency (96%) when compared to the post-inoculation spray of the B. velezensis BP-1 broth. These findings suggest that the optimized fermentation broth of the B. velezensis BP-1 strain had strong antifungal activity. This could be a potent biocontrol tool for aiding in the early disease management of web blotch in peanut plants.