Rhizobacteria from Iraq: A Novel Biocontrol Approach for Tomato Root Rot Disease

Background: Tomato production in Iraq is subject to significant decline due to contamination of agricultural field soils with soil-borne pathogenic fungi, particularly Rhizoctonia solani. Rhizobacteria are the best alternative to chemical fungicides in controlling the disease. Methods: Dual culture approach was employed to assess the antifungal activity of 324 rhizobacterial isolates against R. solani in vitro. Superior antigenic isolates were identified using 16S rRNA, gyrA, gyrB and rpoB gene sequencing. Physiological characteristics such as hydrogen cyanide, protease, chitinase, siderophore and nitrogen fixation of the antigenic isolates were screened. Result: A total of 324 rhizobacterial isolates were extracted from rhizosphere samples, with four isolates demonstrating strong antifungal activity above 66% against R. solani. The isolates were identified as Leclercia adecarboxylata DKS3, Bacillus halotolerans DMC8, Bacillus subtilis NAS1 and Paenibacillus polymyxa TRS4. These isolates demonstrated notable biocontrol and plant growth-promoting traits in vitro, including nitrogen fixation and the generation of protease, chitinase, hydrogen cyanide and siderophores, as well as the solubilization of potassium and phosphate. These attributes are essential for enhancing plant growth and resilience to pathogenic stress. This research highlights the ability of these rhizobacteria to function as effective biocontrol agents and promoters of plant growth in sustainable agriculture.