Bioprospecting of Plant Growth-Promoting Rhizobacteria for the Management of Late Leaf Spot Disease

Biocontrol Potential of Plant Growth Promoting Rhizobacteria against Fusarium oxysporum in Pepper Plants

Aim: This study aimed to examine the biocontrol potential of plant growth-promoting rhizobacteria previously isolated from the tomato rhizosphere against Fusarium oxysporum in pepper plants. Place and Duration of Study: This study was conducted at the Microbiology Laboratory of the Federal University, Oye-Ekiti, between July 2025 and May 2026. Methods: Isolates were obtained from stock cultures and screened for key plant growth-promoting traits, including ammonia, siderophore, nitrogen fixation, and amylase production. Phytopathogenic fungi were isolated from apparently diseased tomato plants. The antifungal activity of the rhizobacterial isolates was evaluated using a dual-culture method. The greenhouse experiment was conducted using a completely randomised block design. Results: Each of the five bacterial isolates exhibited important plant growth-promoting characteristics. Throughout the investigation, isolate IS4A produced the greatest increase in plant height, reaching more than 35 cm by Week 8. By Week 8, isolate IS9 had reached approximately 30 cm, representing the second-highest growth promotion. The highest percentage inhibition of Fusarium was recorded for isolate IS14B (56%), followed by IS13 (47%), IS4A (45%), IS9 (27%), and IS10 (24%). Among all groups, pathogen-inoculated plants (Control 1: Fusarium only) had the lowest fresh weight (5.21 g) and dry weight (0.42 g). IS9 recorded the greatest biomass accumulation, with a fresh weight of 32.12 g and a dry weight of 8.16 g, more than three times the healthy baseline (Control 2: 9.39 g fresh weight and 2.38 g dry weight). Conclusion: The present findings indicate that Pseudomonas lactis and Bacillus tropicus have potential as biological control agents against Fusarium oxysporum while simultaneously promoting pepper growth.

In vitro antagonistic activity of Plant Growth Promoting Rhizobacterial (PGPR) isolates against mulberry charcoal rot pathogen, Macrophomina phaseolina

The charcoal rot caused by Macrophomina phaseolina is the most virulent soil-borne disease in mulberry. Due to the issues of pollution, disparity in soil ecosystem along with possible risks to silkworms, the natural control method known as a promising technique for the management of root diseases. The objective of this study was to evaluate the antifungal efficacy of Plant Growth Promoting Rhizobacteria (PGPR) isolates against M. phaseolina. The charcoal rot causing pathogen, M. phaseolina was isolated from infected mulberry roots and its morphological and microscopical characters were observed. A total of 10 PGPR isolates were purified from healthy mulberry rhizosphere soil and identified isolates were belonging to the genera of Bacillus. The antifungal activity showed that BSSY9 isolate showed maximum growth inhibition of 58.5 % followed by BSKP3 isolate with 54.07%. Hence, thisisolates could be useful in developing an eco-friendly root rot management practices.

Rhizospheric Bacteria from Argan and Raspberry Enhance Tomato Resistance to Fusarium oxysporum

Pathogenic strains of Fusarium oxysporum are major soilborne fungal pathogens responsible for Fusarium wilt in tomato, leading to significant yield losses worldwide. This study evaluated the biocontrol potential of rhizospheric bacterial isolates from argan (Argania spinosa) and raspberry (Rubus idaeus) soils through an integrated approach combining in vitro screening, greenhouse validation, and phylogenetic analysis. A total of 27 bacterial isolates were screened for antifungal activity using dual culture assays, of which ten exhibited more than 50% inhibition of fungal growth. Selected isolates were further evaluated for volatile organic compound (VOC)-mediated inhibition. Despite strong in vitro performance for several isolates, greenhouse experiments revealed that antifungal activity in vitro was not a reliable predictor of in planta efficacy. Among the tested isolates, BSA25, BSA23, and BSF8 significantly reduced disease severity and incidence under greenhouse conditions, with BSA25 achieving the greatest suppression. In addition to disease control, certain isolates promoted plant growth under pathogen stress, indicating dual functionality as plant growth-promoting rhizobacteria (PGPR). Molecular identification based on 16S rRNA gene sequencing and phylogenetic analysis (Neighbor-Joining, Kimura 2-parameter) revealed that the isolates belong to PGPR-associated genera, including Bacillus and Pseudomonas, while also highlighting functional variability among closely related taxa. Overall, this study demonstrates that multi-trait evaluation, integrating mechanistic screening and in planta validation, provides a more reliable framework for selecting effective biocontrol agents. The identified isolates, particularly BSA25, represent promising candidates for further evaluation for sustainable management of Fusarium wilt in tomato production systems.

Isolation and Enumeration of Soil Bacterial Population Associated with Rhizosphere Soils of Yellow Leaf Disease of Arecanut

Yellow Leaf Disease (YLD) is one of the most destructive diseases affecting arecanut, causing severe yield reduction and a decline in palm vigour. The present study was undertaken to isolate, enumerate, and characterise culturable rhizosphere bacterial communities associated with healthy and YLD-affected arecanut palms. Rhizosphere soil samples were collected from healthy and diseased gardens, and bacterial colonies were isolated using serial dilution and the spread-plate technique on nutrient agar medium. The purified isolates were characterised based on colony morphology, Gram reaction, and cell morphology. A total of 33 bacterial isolates were obtained and characterised. Of these, 29 isolates (87.88%) were Gram-positive, whereas only four isolates (12.12%) were Gram-negative, indicating the predominance of Gram-positive bacteria in the arecanut rhizosphere. Colony morphology exhibited considerable diversity in colour and shape, with predominantly circular (73%) and serrated (27%) colonies. Microscopic examination revealed both cocci and rod-shaped bacterial cells. The predominance of Gram-positive bacteria and the higher culturable bacterial population in healthy rhizosphere soils suggest the presence of microbial communities that may contribute to nutrient cycling, plant growth promotion, and the suppression of soil-borne pathogens. These findings provide baseline information on culturable bacterial diversity associated with healthy and YLD-affected arecanut rhizospheres.

Efficiency of some Types of Bacteria Associated with Cucumber Roots Against the Rhizoctonia Solani

Biological control of wheat root rot using rhizosphere isolates of Bacillus sp. and Trichoderma harzianum

Abstract Soil-borne fungal pathogens significantly limit wheat production in Kazakhstan, particularly Fusarium solani (Mart.) Sacc. 1881 and Bipolaris sorokiniana (Sacc.) Shoemaker, 1959, which cause root rot and early seedling decline. This study aimed to isolate and characterize indigenous rhizosphere antagonists with biocontrol potential against these pathogens and to evaluate their effects on wheat seed germination and early growth. More than 20 microbial isolates were obtained from the rhizosphere of winter wheat. Two active antagonistic strains were selected by dual-culture assays: Bacillus sp. NK1 and Trichoderma harzianum S1. Inhibition zones against F. solani reached 23.75 ± 0.67 mm for NK1 and 32.89 ± 0.67 mm for S1. Cell-free culture supernatants significantly reduced mycelial growth and completely inhibited spore germination. Molecular identification based on 16S rRNA sequencing and TEF-1α/RPB2 analysis confirmed the taxonomic affiliation of both isolates. Seed treatment significantly improved germination (88%), root length, shoot length, and seedling vigor compared with untreated controls (P < 0.01). In pot experiments, both strains promoted biomass accumulation and improved seedling growth under pathogen pressure, with the Bacillus strain showing the strongest growth-promoting effect. Combined inoculation did not result in a synergistic response. These findings highlight the potential of indigenous rhizosphere microorganisms as biological control agents for the management of wheat root rot pathogens.