Isolation, Identification and Determination of Biocontrol Activities of Rhizobacteria against Cown Rot Disease Agent Rhizoctonia solani AG 2-2 in Sugar Beet (Beta vulgaris L.)

This study aims to investigate the biocontrol potential of antagonistic and plant growth-promoting rhizobacteria (PGPR) isolated from plant roots and soils against the crown rot pathogen Rhizoctonia solani AG 2-2 in sugar beet (Beta vulgaris L.) tubers. A total of 219 soil samples were collected from 20 provinces to obtain putative bacterial PGPR isolates that could potentially be used as biological control agents (BCAs). A total of 752 bacterial isolates were obtained, and there in vitro antifungal activity against R. solani AG-2.2 was tested in double culture experiments. The result was that 117 PGPR bacterial isolates exhibited antibiotic properties that inhibited mycelial growth of the fungal pathogen. These isolates were also characterized for their antagonistic and plant growth-promoting properties, including phosphorus solubility, hydrogen cyanide (HCN) activity, siderophore production, ACC deaminase activity, and indole-3-acetic acid (IAA) production. The 12 best PGPR isolates were then subjected to an in vivo pot test using a weighted scoring system. The isolate Bacillus subtilis 119.2 was identified as the most effective isolate that completely inhibited the outbreak of the disease caused by R. solani AG-2.2 in sugar beet. Considering the results of the in vitro and in vivo studies, the B. subtilis 119.2 isolate showed its potential as an environmentally friendly biological control agent against R. solani in sugar beet. Overall, B. subtilis 119.2 is a PGPR isolate with potential for use as a biofertilizer or biofungicide.