Abdessamad Elaasri

The two-spotted spider mite, Tetranychus urticae Koch, is a highly polyphagous and economically important pest affecting a wide range of crops worldwide. This study evaluated the potential of four rhizobacterial isolates—Leucobacter aridicollis (IQR1), Paenochrobactrum sp. (IQR2), uncultured bacterium IQR3, and marine bacterium AK6_052 (IQR5)—as candidate biological control agents against T. urticae. The rhizobacterial isolates were obtained from the tomato rhizosphere at the INRA experimental farm (Agadir, Morocco) and evaluated for their acaricidal and repellent activities against T. urticae. Corrected mortality and repellency index were assessed after 24, 48, and 72 h of exposure. All four isolates exhibited acaricidal activity, with IQR3 and IQR5 showing the greatest efficacy. Corrected mortality reached 69.9% with IQR3 at the highest concentration after 72 h of exposure. The isolates showed no statistically significant repellent activity. Under greenhouse conditions (10⁸ CFU mL⁻¹), IQR3 was associated with the lowest infestation incidence (64%), the lowest infestation severity (13.3%) and the lowest adult density (1.8 adults leaf⁻¹); IQR5 showed a comparable trend. Overall, IQR3 and IQR5 represent promising rhizobacterial candidates for the sustainable management of T. urticae in tomato production. Further studies are needed to optimize their formulation, elucidate their mechanisms of action, and validate their efficacy under field conditions.

Plant growth-promoting rhizobacteria (PGPR) offer a sustainable strategy for enhancing crop productivity and suppressing phytopathogens. In this study, seven bacterial isolates obtained from the rhizosphere of healthy tomato plants were evaluated for their antagonistic activity against the fungal pathogen Passalora fulva, the leaf miner Tuta absoluta, and their effects on tomato growth. In vitro dual-culture assays revealed that isolates IQR1, IQR2, IQR3, and IQR5 significantly inhibited P. fulva mycelial growth, with inhibition rates exceeding 35%. Volatile organic compounds (VOCs) produced by the bacterial isolates exhibited considerable antifungal activity, with IQR5, IQR1, and IQR2 achieving over 84% inhibition. Molecular identification based on 16S rDNA sequencing indicated that these isolates belong to distinct taxa: Leucobacter aridicolis (ON799334.1) (genus Leucobacter), Paenochrobactrum sp. (JF804769.1) (genus Paenochrobactrum), an uncultured bacterium (JQ337400.1) (genus Psychrobacter), and marine bacterium AK6_052 (KF816539.1) (genus Brevundimonas). Under greenhouse conditions, isolates IQR3, IQR5, and IQR1 reduced disease incidence of P. fulva to 20–26%. The same isolates also promoted plant growth, enhancing stem height and collar diameter. In addition, IQR5 significantly reduced T. absoluta larval density and foliar damage, with the number of larvae per leaflet decreasing to 1.42, compared to 3.20 in the control. These findings highlight the potentials of these rhizobacterial strains—particularly IQR5—as effective biocontrol agents and biofertilizers for integrated pest and disease management in tomato cultivation.