POTENTIAL OF SOME PLANT GROWTH-PROMOTING RHIZOBACTERIAL STRAINS AS BIOCONTROL AGENTS AGAINST FUSARIUM WILT DISEASE IN CUCUMBER

Abstract

: Herein, three Fusarium; oxysporum strains were isolated from infected cucumber-wilt roots and showed disease severity with the percentages of 73%, 66%, and 51%. The F. oxysporum exhibited the highest wilt disease was selected to investigate the biocontrol efficacy of plant growth-promoting rhizobacteria. To achieve this goal, three rhizobacterial strains were isolated and identified as Achromobacter xylosoxidans Ck2 , Bacillus haynesii Ck5, and Bacillus paramycoides Ck7. These strains showed efficacy to inhibit the growth of F. oxysporum in-vitro with percentages of 56.2±0.2, 51.3±0.3, and 46.2±0.4% for Ck2, Ck5, and Ck7, respectively. These rhizobacterial strains showed nitrogen-fixing activity assayed by acetylene reduction and phosphate-solubilizing with values of (446.9±1.6, 310.8±1.9, and 213.6±1.2 n-moles-C 2 H 4 /mL/24h) and (183.6±1.1, 192.3±1.3, and 34.29±1.2 μg mL -1 ) for Ck2, Ck5, and Ck7, respectively. Moreover, these strains showed plant growth-promoting properties including ammonia, hydrogen cyanide (HCN), siderophores, hydrolytic enzymes, and phytohormones production. Under greenhouse conditions, the rhizobacterial strains Ck2, Ck5, and Ck7, and their consortium had the efficacy to protect cumber from wilt disease caused by F. oxysporum with percentages of 67.6, 63.2, 58.7, and 75.7%, respectively. Whereas the highest growth performance and the highest wilt protection (79.1%) of F. oxysporum- infected cucumber was attained in presence of bacterial consortium under field conditions.