Yacine Goudjal

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 Streptomyces genus and five were non-Streptomyces. All isolates were screened for their in vitro antifungal activity against Rhizoctonia solani. The six that had the greatest pathogen inhibitory capacities were subsequently tested 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 seeds with 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 as thioperoxydicarbonic diamide, tetramethylthiram (TMTD) and no significant differences (P<0.05) were observed. 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 position based on 16S rDNA sequence analysis and phylogenetic studies indicated that the strains CA-2 and AA-2 were related to Streptomyces mutabilis NBRC 12800(T) (100% of similarity) and Streptomyces cyaneofuscatus JCM 4364(T) (100% of similarity), respectively.

Antifungal properties of an actinomycin D‐producing strain, Streptomyces sp. 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%.

Biocontrol Capacities and Plant Growth-Promoting Traits of Endophytic Actinobacteria Isolated from Native Plants of Algerian Sahara

Fusarium root rot is one of the most important plant diseases. Chemical fungicides are efficient but they have been much criticized. The present study investigates endophytic actino-bacteria isolated from native plants of the Algerian Sahara in the aim of assessing their ability to exercise biocontrol over this soil-borne fungus, and to highlight their plant growth-promoting traits on seedlings of tomato cv. Mar-mande. A total of 21 endophytic actinobacteria were isolated from plant roots. Six isolates were first selected for the biocontrol trials on the basis of their antifungal properties. In vivo biocontrol activity was measured by the disease incidence on plants grown in infested soils. Four isolates decreased the disease incidence in both sterilized and non-sterilized infested soils, whereas no significant differences were obtained with the control chemical agent. Indole-3-acetic acid and siderophore production, and phosphate solubilization were investigated as plant growth-promoting traits. The isolate ZL2 showed positive results for these mechanisms. Statistical treatment of the data brought out the potential of this isolate as a promising candidate for the biocontrol of root rot in tomato seedlings and in regard to its plant growth-promoting characteristics. Molecular identification was performed by 16S rRNA gene sequence analysis and indicated that Streptomyces sp. ZL2 was related to Streptomyces caeruleatus (99.6% of similarity). Isolate Streptomyces sp. ZL2 enhanced the plant resistance to F. oxysporum f. sp. radicis lycopersici root rot and promoted the growth of tomato seedlings. These properties open up promising perspectives for the possible application of isolate ZL2 in crop protection.

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

ABSTRACT 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

ABSTRACT 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.

Endophytic Actinobacteria from Native Plants of Algerian Sahara: Potential Agents for Biocontrol and Promotion of Plant Growth

Abstract Actinobacteria are widely represented in soils, and play various beneficial roles. They can occur in the plant rhizosphere soil and inhibit soil-borne pathogens. Some actinobacteria are also known to form close associations with plants, colonize their internal tissues without causing disease symptoms, induce systemic resistance, and promote their growth. In the aim of discovering new biocontrol and/or plant growth-promoting agents, researchers have turned their attention to rhizospheric and endophytic actinobacteria isolated from different ecological niches. In the Algerian Sahara, several native plants have successfully adapted to the drought of arid climate and the poor sandy soil. The regeneration from seeds and the vigorous growth without human intervention suggests a contribution of beneficial actinobacteria, both to the biological protection of seedlings against soil-borne phytopathogens and to promote their growth. Recent knowledge in the field of isolation and selection of promising actinobacteria associated with roots of Saharan native plants, their biocontrol and plant growth-promoting attributes, their efficacy in the in vivo biocontrol of soil-borne phytopathogens and in the growth promotion of crop plants, and proposals of formulated biofungicides for sustainable agriculture are explored in this chapter.

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

ABSTRACT 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.