Potential of endophytic Streptomyces spp. for biocontrol of Fusarium root rot disease and growth promotion of tomato seedlings

Sixteen endophytic actinobacteria isolated from roots of native plants were evaluated for their antagonistic potential against soil-borne phytopathogenic fungi. Among them, three strong antagonistic isolates were selected and characterised for in vitro plant-growth-promoting and biocontrol traits, including production of hydrogen cyanide, indole-3-acetic acid and siderophores, chitinase and β-1,3-glucanase activities, and inorganic phosphate solubilisation. In all trials, the strain Streptomyces sp. SNL2 revealed promising features. The selected actinobacteria were investigated for the biocontrol of Fusarium oxysporum f. sp. radicis lycopersici and for growth promotion of tomato (Solanum lycopersicum L. cv. Aïcha) seedlings in autoclaved and non-autoclaved soils. All seed-bacterisation treatments significantly reduced the root rot incidence compared to a positive control (with infested soil), and the isolate SNL2 exhibiting the highest protective activity. It reduced the disease incidence from 88.5% to 13.2%, whereas chemical seed treatment with Thiram® provided 14.6% disease incidence. Furthermore, isolate SNL2 resulted in significant increases in the dry weight, shoot and root length of seedlings. 16S rDNA sequence analysis showed that isolate SNL2 was related to Streptomyces asterosporus NRRL B-24328T (99.52% of similarity). Its interesting biocontrol potential and growth enhancement of tomato seedlings open up attractive uses of the strain SNL2 in crop improvement

Development of formulations based on Streptomyces rochei strain PTL2 spores for biocontrol of Rhizoctonia solani damping-off of tomato seedlings

Rhizoctonia solani is one of the most problematic soil-borne pathogenic fungi for several crop cultures worldwide. This study highlights the effectiveness of high-antagonistic Streptomyces rochei strain PTL2, isolated from root tissues of Panicum turgidum, in controlling the R. solani damping-off and growth promotion of tomato (cv. Marmande) seedlings. The isolate PTL2 was characterised for in vitro biocontrol and plant growth-promoting traits. It exhibited remarkable positive results in all trials, including production of hydrogen cyanide, siderophores, 1-aminocyclopropane-1-carboxylate deaminase and phytohormones, chitinolytic activity and inorganic phosphate solubilisation. PTL2 spores were formulated as wettable talcum powder, sodium alginate pellets and sodium alginate-clay pellets. Their abilities in the biocontrol of R. solani and plant growth promotion were investigated in autoclaved and non-autoclaved soils. Talcum powder and sodium alginate pellets significantly reduced the damping-off severity index compared to a positive control. The talcum powder exhibited the highest protective activity, reducing the disease incidence from 89.3% to 14.1%, whereas chemical seed treatment with Thiram® provided a disease incidence of 16.7%. Furthermore, the talc-based powder formulation resulted in greatest increases in the root length, shoot length and dry weight of seedlings. The interesting biocontrol potential and growth enhancement of tomato seedlings open up promising perspectives for the possible application of talcum powder formulation based on PTL2 spores in crop improvement

Plant-growth-promoting potential of endosymbiotic actinobacteria isolated from sand truffles (Terfezia leonis Tul.) of the Algerian Sahara

Seven endosymbiotic actinobacteria were isolated from sand truffles (Terfezia leonis Tul.) harvested in the Hassi R’Mel region of the Algerian Sahara. Morphological characteristics and chemotaxonomical analysis indicated that all isolates were members of the Streptomyces genus. All the isolated actinobacteria were initially screened in vitro for antifungal capacities, chitinolytic activities, siderophore production, and synthesis of plant-growth regulators (indole-3-acetic acid and gibberellic acid). The isolate Streptomyces sp. TL7 exhibited a remarkable profile with positive results in all trials, while the others showed variable responses to assays. In vivo trials were then carried out with the isolates to evaluate their root colonization abilities and plant-growth-promoting potential on tomato (cv. Marmande) seedlings. The results showed that all these Streptomyces strains could be isolated successfully from inside the roots of inoculated tomato seedlings. However, the plant-growth-promoting effect varied depending on the treatment. Seeds surface-coated with spores of Streptomyces sp. strain TL7 showed the highest performance, with significantly increased (P < 0.05) shoot and root lengths, and seedling fresh and dry weights. The taxonomic position based on 16S rDNA sequence analysis and phylogenetic studies indicated that strain TL7 was related to Streptomyces neopeptinius KNF 2047T (99.0 % similarity). The interesting antifungal properties and plant-growth promotion traits shown by Streptomyces sp. strain TL7 may indicate a potential for its possible use as plant-growth-promoting agent, especially for tomato seedlings

Biocontrol and plant growth promoting properties of Streptomyces mutabilis strain IA1 isolated from a Saharan soil on wheat seedlings and visualization of its niches of colonization

In this study, the biocontrol ability and colonization behavior of a highly antagonistic Streptomyces mutabilis strain, named IA1, recently isolated from a Saharan soil, were assessed on wheat seedlings. In this study we showed that strain IA1 secretes IAA and GA3 and is able to enhance growth of wheat seedlings. Using DOPE-FISH coupled with confocal laser scanning microscopy (CLSM), we observed moreover that following caryopsis inoculation and plant growth the strain can colonize the rhizoplane, the surface of caryopsis as well as the endorhiza, crossing from the rhizodermis up to the vascular system. Interestingly, further visualizations revealed that the actinobacterial strain could also be endophytic inside the caryopsis up to the endocarp layer (the dried fruit part, not the seed part of grain). Disease caused by Fusariumculmorum was further evaluated on seedlings and results showed that coated seeds with strain IA1 can reduce both disease occurrence (64.7%) and decrease severity (79.6%). This study showed that strain IA1 derived from a Saharan soil could protect a temperate crop from F. culmorum seedling blight, promote growth and colonize various niches on the surfaces of the phytosphere (roots, seeds) as well as plant endosphere compartments

Biocontrol of Rhizoctonia solani damping-off and promotion of tomato plant growth by endophytic actinomycetes isolated from native plants of Algerian Sahara

Thirty-four endophytic actinomycetes were isolated from the roots of native plants of the Algerian Sahara. Morphological and chemical studies showed that twenty-nine isolates belonged to the Streptomycesgenus and five were non-Streptomyces. All isolates were screened for their in vitro antifungal activityagainst Rhizoctonia solani. The six that had the greatest pathogen inhibitory capacities were subsequentlytested for their in vivo biocontrol potential on R. solani damping-off in sterilized and non-sterilized soils,and for their plant-growth promoting activities on tomato seedlings. In both soils, coating tomato seedswith antagonistic isolates significantly reduced (P < 0.05) the severity of damping-off of tomato seedlings.Among the isolates tested, the strains CA-2 and AA-2 exhibited the same disease incidence reduction asthioperoxydicarbonic diamide, tetramethylthiram (TMTD) and no significant differences (P < 0.05) wereobserved. Furthermore, they resulted in a significant increase in the seedling fresh weight, the seedling length and the root length of the seed-treated seedlings compared to the control. The taxonomic positionbased on 16S rDNA sequence analysis and phylogenetic studies indicated that the strains CA-2 AA-2were related to Streptomyces mutabilis NBRC 12800ᵀ(100% of similarity) and Streptomyces cyaneofuscatus JCM 4364ᵀ(100% of similarity), respectively

Biocontrol and plant-growth-promoting capacities of actinobacterial strains from the Algerian Sahara and characterisation of Streptosporangium becharense SG1 as a promising biocontrol agent

Sixteen actinobacterial strains isolated from various ecological niches in the Algerian Sahara were screened for their biocontrol potential in root rot disease caused by Fusarium culmorum and their promotion of durum wheat growth. All actinobacteria were studied for in vitro antagonistic activity and plant-growth-promotion traits, for the production of cyanhydric acid, siderophores, chitinases and indole-3-acetic acid, and for the solubilisation of inorganic phosphate. Strongly antagonistic actinobacteria were selected for the biocontrol of F. culmorum in vivo and for the growth promotion of durum wheat plants in autoclaved and non-autoclaved soils. The Streptosporangium becharense strain SG1 exhibited remarkable positive results in all trials. Compared to untreated wheat seeds, the root rot severity index was decreased significantly (P < 0.05) by all seed bacterization treatments. However, the highest protective effect was obtained by the strain SG1, which reduced the disease severity index from 77.8% to 16%, whereas it was only reduced to 24.2% by chemical seed treatment with Dividend®. Moreover, strain SG1 led to significant increases in the shoot length, root length and dry weight of plants, thus opening up interesting perspectives for possible exploration in crop enhancement

Antifungal properties of an actinomycin D-producing strain,Streptomycessp. IA1, isolated from a Saharan soil

An actinomycete strain named IA1, which produced an antimicrobial compound, was isolated from a Saharan soil in In Amenas, Algeria. The study of the 16S rDNA sequence of this strain permitted to relate it to Streptomyces mutabilis NBRC 12800T (99.93% of similarity). Strain IA1 exhibited strong activity against a wide range of plant pathogenic fungi. One bioactive compound produced in large amounts (46.7 mg L−1 day−1), named YA, was isolated and purified by TLC and reverse phase HPLC. The structure elucidation of the pure substance, using combined data from UV visible, NMR spectra, and mass spectrometry, permitted to identify it as actinomycin D, and was thus found for the first time in S. mutabilis related species. The biocontrol abilities of the strain IA1 and compound YA were evaluated through two diseases, i.e., chocolate spot of field bean and Fusarium wilt of flax. The occurrence of the two fungal diseases was effectively reduced. The reduction of chocolate spot disease symptoms reached 80 and 91.7% with IA1 and YA seedlings pretreatments, respectively. Soil pretreatment with IA1 or YA also allowed to reduce Fusarium wilt disease impact by almost 60%

Endophytic actinomycetes from spontaneous plants of Algerian Sahara: indole-3-acetic acid production and tomato plants growth promoting activity

Twenty-seven endophytic actinomycete strains were isolated from five spontaneous plants well adapted to the poor sandy soil and arid climatic conditions of the Algerian Sahara. Morphological and chemotaxonomical analysis indicated that twenty-two isolates belonged to the Streptomyces genus and the remaining five were non- Streptomyces. All endophytic strains were screened for their ability to produce indole-3-acetic acid (IAA) in vitro on a chemically defined medium. Eighteen strains were able to produce IAA and the maximum production occurred with the Streptomyces sp. PT2 strain. The IAA produced was further extracted, partially purified and confirmed by thin layer chromatography (TLC) analysis. The 16S rDNA sequence analysis and phylogenetic studies indicated that strain PT2 was closely related to Streptomyces enissocaecilis NRRL B 16365T, Streptomyces rochei NBRC 12908T and Streptomyces plicatus NBRC 13071T, with 99.52 % similarity. The production of IAA was affected by cultural conditions such as temperature, pH, incubation period and L-tryptophan concentration. The highest level of IAA production (127 lg/ml) was obtained by cultivating the Streptomyces sp. PT2 strain in yeast extract-tryptone broth supplemented with 5 mg L-tryptophan/ ml at pH 7 and incubated on a rotary shaker (200 rpm) at 30°C for 5 days. Twenty-four-hour treatment of tomato cv. Marmande seeds with the supernatant culture of Streptomyces sp. PT2 that contained the crude IAA showed the maximum effect in promoting seed germination and root elongation

The role of plant growth promoting bacteria on arsenic removal: a review of existing perspectives

Phytobial remediation is an innovative tool that uses plants and microbes to mitigate Arsenic (As) contamination of the environment. Recently, plant growth-promoting bacteria (PGPB) that assists phytoremediation has been highly touted for both improving plant metal tolerance and promoting plant growth while achieving the goal of large-scale removal of As. This review focuses on the PGPB characteristics influencing plants and the mechanisms in which they function to overcome/lessen As-induced adversities. Several recent examples of mechanisms responsible for increasing the availability of As to plants and coping with As stresses facilitated by PGPB will be reviewed. Although drawbacks to phytoremediation have been reported, encouraging results have been developed with regular monitoring. Introducing PGPB-assisted phytoremediation of As in a field requires an assessment of the environmental effects of PGPB, especially with respect to the impacts on indigenous bacteria