Biocontrol of soil‐borne plant pathogens attacking cucumber (Cucumis sativus) by Rhizobacteria in a semiarid environment

Abstract

Three new strains of growth‐promoting N₂‐fixing rhizobacteria, namely, Azospirillum brasilense SBR, Azotobacter chroococcum ZCR, and Klebsiella pneumoneae KPR, engineered for increased N₂ fixation, and a commercial product H ALEX® were tested for growth promotion and as remediation agents against the soil‐borne plant pathogens Fusarium oxysporum f. sp. lycopersici, Rhizoctonia solani and Pythium sp., which attack cucumbers in the semiarid environment of Egypt. In vitro, the bacteria reduced the dry weight of mycelium of Fusarium by 90–96%, that of Rhizoctonia by 72–94%, Pythium by 71–95%, and Sclerotinia by 100%. Bioassaying the effect of HALEX on the pathogens showed a 56% decrease in the incidence of damping‐off and a 66% decrease in flowering at the age of 8 weeks. It showed an increase in emergence by 4%, photosynthetic area by 22%, shoot and root dry weights by 30% and 80%, respectively, and shoot N content by 89%. The term Sigmoid nutrition is introduced to describe the continuous and close provision of growth promoters and nutrients to the plant all along the Sigmoid growth curve.

Key words:

• Azospirillum
• Azotobacter
• damping‐off
• dry weight
• emergence percentages
• Fusarium
• induced systemic resistance
• Klebsiella
• plant growth promotion
• Pythium
• Rhizoctonia
• Sclerotinia
• seed inoculation
• total nitrogen