Antagonistic bacteria contribute to the management of plant diseases by stimulating the natural defenses in the host and/or by ensuring direct biocontrol of the aggressors. The objective of this work was to isolate, identify and evaluate (in vitro) various Bacillus spp. for their potential to control phyopathogenic fungi. Selection of the 40 strains of Bacillus previously isolated from the soil in various areas of western Algeria was carried out by direct confrontation on the mycelial growth of four phytopathogens (Fusariumoxysporumf.splycopersici, Alternaria tenuis , Phytophthorainfestans, Ascochytapisi). This strategy involved using the antagonistic potential of microorganisms found in the plant environment in Algeria. The second part of this work consisted of the characterization and identification of tested strainsThe identification of the selected strains was carried out by biochemical tests. The results obtained showed that at the end of the fifth day, the most promising isolates showed antifungal activity and reached an inhibition rate of the mycelial growth of phytopathogenic fungi, respectively, F. oxysporumf. splycopersici 75%, A. tenuis 80%, P. infestans 83.30%, Ascochytapisi 67%. The potential antagonist of Bacillus tested in vitro by direct confrontation against 04 phytopathogenic fungi showed that all strains of Bacillus decreased fungal mycelial growth. Two strains of Bacillus B30 and B41 were found to have the most efficacy against Fusarium oxysporum f.sp. lycopersici, Alternaria tenius, Phytophtora infestans et Ascochyta pisi, with an inhibition rate of 65.25 and 72.25% respectively These results demonstrate that Bacillus sp. presenteds a potential for biological control. However, it is important to understand the mechanisms implemented by these bacteria to develop effective protection strategies.
Cactus are among the most drought tolerant plants. As Opuntia is able to grow under the stress of drought, this study aims to check if endophytic bacteria isolated from cactus roots have beneficial potential for crops such as wheat during drought. Two endophytic bacterial isolates were isolated from the roots of the cactus and screened for their plant growth promoting characteristics, such as N-free growth and auxin production. These bacteria have demonstrated their potential to promote the growth of durum wheat under in-vitro conditions and have been identified as Pseudomonas putida and P.brassicacearum, following the sequencing of the 16S rRNA gene and phylogenetic analysis, and significantly improved growth parameters such as seeding length compared to the unobstructed control. After 05 days of contact of the two bacteria, P.putida and P.brassicacearum, with sprouted wheat seeds, a root growth rate of (39.88% and 62.14%, respectively) was recorded. The same effect on the growth of wheat roots is caused by the volatile substances of these bacteria deposited separately, with a rate of (53.30% and 24.18%) respectively. Symptoms of drought stress were visibly reduced on seedlings inoculated with P.putida and P.brassicacearum bacteria, a result supported by a growth rate of root parameters in length (260.83% and 179.60%), surface (21.98% and 60.17%) and scope (59.46% and 62.67%), respectively. This work opens up many perspectives for the characterization and selection of endophyte bacteria of under-used drought-tolerant species such as cacti for the improvement of the growth of field crops. These results promote the deployment of Pseudomonas sp as an effective biofertilizer in wheat.
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